MEAaH  SCIENCE 


HX64085635 
QM451  .V71  Brain  and  spinal  cor 


EMILVILLIGER 
BRAIN  AND  SPINAL  CORD 

PIERSOL 


OMASL 


Mli 


Columbia  ®nttiers(ttp 

COLIEGE  OF 

PHYSICIANS  AND  SURGEONS 

LIBRARY 


cop 


,z 


DR.  C.  G.  DYKE 


Digitized  by  tine  Internet  Arciiive 

in  2010  witii  funding  from 
Columbia  University  Libraries 


http://www.archive.org/details/brainspinalcordOOvill 


BRAIN 
AND  SPINAL  CORD 

A  MANUAL  FOR  THE  STUDY  OF  THE  MORPHOLOGY  AND 
FIBRE-TRACTS  OF  THE  CENTRAL  NERVOUS  SYSTEM 


BY 

DR.  MED.  EMIL  VILLIGER 

PRIVATDOZENT  IN    NEUROLOGY  AND   NEUROPATHOLOGY  IN  THE   UNIVERSITY  OF  BASEL 


TRANSLATED  BY 

GEORGE  A.  PIERSOL,  M.D.,  Sc.D. 

PROFESSOR  OF  ANATOMY  IN  THE  UNIVERSITY  OF  PENNSYLVANIA 


FROM  THE  THIRD  GERMAN  EDITION 
WITH  2S2  I L LUSTRA  TIONS 


PHII.At)ELPHIA  &  LONDON 

J.  B.  LIPPINCOTT   COMPANY 


Copyright,   1912,  by  J.  B.  Lippincott  Co. 


TRANSLATOR'S  NOTE 


The  increasing  attention  given  to  the  study  of  the  Central  Nervous  System  has 
emphasized  the  need  of  a  suitable  guide  for  laboratory  exercises.  The  usefulness  of 
Dr.  Villiger's  excellent  manual  has  been  greatly  increased  by  the  addition  of  Part  III, 
illustrating  the  architecture  of  the  brain-stem  by  series  of  consecutive  sections,  which 
first  appeared  in  the  second  edition.  While  of  much  assistance  to  the  student  in  identi- 
fying details  under  the  microscope,  the  series  so  well  represents  the  actual  preparations, 
that  close  study  of  the  illustrations  alone  will  amply  repay  where  satisfactory  specimens 
are  inaccessible. 

The  translator  has  respected  the  author's  desire  to  retain  the  brevity  and  clearness 
which  characterize  the  book  ;  he  has  refrained,  therefore,  from  amplifying  the  text, 
which  appears,  with  slight  changes,  as  in  the  original.  Through  the  courtesy  of  the 
firm  of  Wilhelm  Engelmann,  of  Leipzig,  in  supplying  advance  proofs,  it  has  been  pos- 
sible to  include  the  new  figures,  which  have  been  added  to  the  third  German  edition. 
The  selected  bibliography,  appended  by  the  translator,  will  be  of  service,  it  is  hoped, 
to  those  desirous  of  consulting  the  original  papers  or  the  more  comprehensive  works 
pertaining  to  the  Central  Nervous  System. 

Philadelphia, 

September,  191 2. 


0 


PREFACE  TO  THE  THIRD  EDITION 


The  cordial  reception  accorded  the  second  edition  has  rendered  necessary,  within 
a  short  time,  issuing  a  new  edition.  Radical  changes  or  amplifications,  notably  the 
desired  additions  to  the  series  of  microscopical  representations  of  brain  sections,  could 
not  be  undertaken.  Notwithstanding  the  first  intention  to  print  the  edition  without 
alterations,  the  hearty  cooperation  of  the  publishers  has  made  it  possible  to  introduce, 
particularly  in   Part   II,   some   new   figures,   to  which   I  wish   to   direct   especial    attention. 

E.  VILLIGER. 
Basel, 

April,  1912. 


AUTHOR'S    PREFACE 


The  second  edition  presents  substantial  changes.  While  some  sections,  pertaining 
to  morphology  as  well  as  to  fibre-tracts,  have  been  simplified  and  made  clearer,  others 
have  been  treated  with  greater  completeness.  Certain  figures  have  been  replaced  by- 
better  ones,  and  many  new  ones,  relating  to  the  paths  of  conduction,  have  been  added. 
The  chief  change,  however,  lies  in  the  addition  of  Part  III,  in  which  I  have  attempted 
to  meet  the  often  expressed  wish,  that  the  conduction-paths  be  represented  not  only  by 
diagrams,  but  also  by  microscopical  pictures.  I  am  well  aware  that  this  third  part 
presents  considerable  gaps.  Unfortunately  at  the  time  only  vertical  sections  through  the 
brain-stem  were  at  my  disposal ;  further,  the  drawing  of  the  new  and  especially  the 
microscopical  illustrations  made  such  claims  upon  me,  that  it  was  impossible  to  satisfy  all 
desires.  Ifevertheless,  I  indulge  the  hope  that  the  study  of  the  fibre-tracts  will  be 
facilitated  by  the  microscopical  representations  now  given  and  by  the  newly  added 
schematic  figures. 

Moreover,  I  wish  particularly  to  emphasize,  that  this  second  edition  remains  a 
manual  and  as  such  is  designed  primarily  to  assist  the  student,  with  all  possible  con- 
ciseness and  clearness,   in  the  study  of  the  anatomy  of  the  central  nervous  system. 

It  is  my  privilege  to   take  this   opportunity   of   expressing   my   sincerest   thanks   to 

Professors  J.    Kollmann  and  N.    K.    Corning  for  their  kindness  in  placing  at   my  disposal 

numerous    microscopical    preparations.       My  especial    acknowledgment    is  due   the  firm  of 

Wilhelm   Engelmann,    of  Leipzig,   whose  cordial  cooperation   enabled  me  to  carry  out  the 

radical    changes    made    necessary    by  the    introduction    of    larger    figures,   particularly  the 

microscopical  illustrations. 

E.  VILLIGER. 


CONTENTS 


PART  I.— MORPHOLOGY. 


Subdivision  of  the  Central  Nervous  System..  3 

Development  of  the  Brain 4 

Development  of  the  Spinal  Cord 8 

Form,  Size  and  Weight  of  the  Brain 9 

General  Consideration  of  the  Brain 11 

Telencephalon — End-Brain 17 

Pallium — Cerebral  Mantle 18 

Rhinencephalon — Olfactory  Brain 25 

1.  Lobus  olfactorius 26 

A.  Lobus  olfactorius  anterior....  27 

B.  Lobus  olfactorius  posterior. .. .  29 

2.  Gyrus  fornicatus 30 

3.  Hippocampus 32 

4.  Gyrus  dentatus 32 

5.  L'ncus  —  Gyrus   uncinatus.     Gyrus 

intralimbicus.       Gyrus     fascio- 

laris 35 

6.  Gyri  Andreje  Retzii 36 

Pars  optica  hypothalami 37 

Internal  Configuration 38 

Gray  Masses  and  Nuclei 46 

Summary  of  Telencephalon 50 

Diencephalon — Inter-Brain 52 

Thalamus  opticus 54 

Pars  mamillaris  hypothalami 56 

Ventriculus  tertius 57 

The  Nuclei  of  the  Diencephalon 58 

Summary 63 


Mesencephalon — Mid-Brain 66 

Lamina  quadrigemina 66 

Pedunculi  cerebri 66 

Aquaeductus  cerebri  (Sylvii) 63 

Gray  Masses  of  the  Mid-Brain 68 

Summary 69 

Isthmus  rhombencephali 70 

Metencephalon 71 

Pons  Varolii 71 

Cerebellum 72 

A.  Lobus  superior 72 

B.  Lobus  posterior 73 

c.  Lobus  inferior 74 

Myelencephalon — Medulla  oblongata 77 

Ventriculus  quartus 79 

Fossa  rhomboidea 81 

Gray  Masses  of  the  Rhombencephalon 82 

Summary  of  the  Rhombencephalon 85 

Brain-Membranes — Meninges 86 

Dura  Mater 87 

Arachnoidea 88 

Pia  Mater 88 

Spinal  Cord — Medulla  spinalis 89 

External  Configuration 89 

Internal  Configuration 90 

Membranes  of  the  Spinal  Cord 93 

Dura  mater  spinalis 93 

Arachnoidea  spinalis 93 

Pia  mater  spinalis 93 


PART  IL— FIBRE-TRACTS. 


Methods  of  Investigating  the  Fibre-Tracts 97 

Histogenesis  of  the  Nervous  System 102 

Development  of  the  Ependyma  and  Neu- 
roglia Cells 103 

Development  of  the  Nerve-Cells 105 

Development  of  the  Cells  of  the  Cerebro- 
spinal Ganglia  and  of  the  Sympathetic 

Ganglia 105 

The     Formed     Elements     of    the     Nervous 

System 106 

A   The  Support-Cells  106 

B.  The  Nerve-Cells  107 

Microscopical    Structure     of     the     Cerebral 

Cortex 114 

I.  Cortex  of  the  Pallium 114 


II.  Rhinencephalon 118 

Bulbus  olfactorius 1 18 

Gyrus  fornicatus 119 

Hippocampus  and  Gyrus  dentatus. ...   1 20 

Hippocampus 121 

Gyrus  dentatus 122 

Cerebral  Localization 123 

The  Motor  Centre 124 

The  Sensory  Centres — Sense-Centres  ...    1 26 

The  Speech  Centres 1 28 

General  Division  of  the  Paths  of  Conduction ...   131 
Conduction  Paths  of  the  Telencephalon 134 

1.  Association  Fibres 134 

2.  Commissural  Fibres 135 

3.  Projection  Fibres 135 


CONTENTS. 


A.  Short  Paths 135 

B.  Long  Paths 137 

Radiatio  corporis  striati 144 

Connections  of  the  Corpus  Striatum 144 

Fibre-Tracts  of  the  Rhinencephalon 144 

1.  Peripheral  Tract 144 

2.  Central  Tract 145 

A.  Connection   of    the    bulbus   olfac- 

torius       with       the       primary 
centres 145 

B.  Connection  of  the  primary  centres 

with   the    secondary   or  cortical 
centres 145 

3.  Connection  of  the  two  primary  centres  149 

4.  Further    connections     of    the    primary' 

centres 149 

5.  Connection     of      the      two      cortical 

centres 149 

6.  Further    connections     of    the    cortical 

centres 149 

Conduction  Paths  of  the  Diencephalon 150 

Conduction  Paths  of  the  Mesencephalon 151 

Conduction  Paths  of  the  Metencephalon 154 

Microscopical  structure  of  the  Cerebellar 

Cortex  and  Fibre-Tracts 154 

Spinal  Cord   159 

The  Gray  Matter 159 

The  White  Matter 160 


1.  Paths  of  the  Anterior  Column   ....   i5i 

2.  Paths  of  the  Lateral  Column 161 

3    Paths  of  the  Posterior  Column  ....   163 

Medulla  Oblongata 166 

Origin  of  the  Cerebral  Nerves 172 

Nervus   olfactorius j  72 

Nervus  opticus 172 

Nervus  oculomotorius 175 

Nervus  trochlearis 176 

Nervus  abducens 176 

Nervus  trigeminus 176 

Nervus    facialis    and   Nervus  intermedius 

Wrisbergi 1 78 

Nervus  acusticus 179 

1.  Nervus  cochleae 179 

2.  Nervus  vestibuli i8r 

Nervus  glossopharyngeus  and  vagus 184 

Nervus  accessorius 185 

Nervus  hypoglossus 186 

General  Survey  of  the  Principal  Paths 186 

A.  Projection  Paths 186 

L  Centripetal  Paths 186 

1.  Ascending  sensory  spinal  paths  i85 

2.  Sensorj'  paths  of  the  cerebral 

nerves 1S8 

n.  Centrifugal  Paths 191 

B.  Reflex  Paths 192 

c.  Association  Paths 197 


PART  III.— SERIAL  SECTIONS  OF  THE  BRAIN-STEM. 


From  ,the  anterior  end  of  the  corpus  cal- 
losum  to  the  quadrigeminal  region 205 


B.  From  the  caudal  part  of  the  medulla  oblon- 
gata to  the  quadrigeminal  region 235 


PART  I. 

MORPHOLOGY. 


BRAIN  AND  SPINAL  CORD 


MORPHOLOGY 


Medullary  plate 


Ciiticle-flate 


medullary  groove 


The  brain  and  the  spinal  cord  together  constitute  the  central  nervous  system 
(systema  nervorum  cetitrale^. 

The  brain  (enccphalon)  is  that  part  of  the  central  nervous  system  lodged  within 
the  cranial  case;  the  spinal  cord,  {medu/la  spinalis)  is  that  part  within  the  vertebral 
canal.  The  boundary  between  the  two  is  neither  macroscopically  nor  microscopically 
sharply  defined.  The  lowest  segment  of  the  brain  corresponds  perfectly  in  form  and 
structure  with  the  uppermost  one  of  the  spinal  cord 
and  is  called,  therefore,  medulla  oblongata — the  length- 
ened marrow.  An  approximate  coarse  boundary  line 
is  supplied  by  the  lowest  bundle  of  the  so-called 
pyramidal  decussation,  or  by  the  highest  root-bundle 
of  the  first  cervical  nerve. 

A  further  separation  of  the  brain  into  different 
segments  is  best  accomplished  by  embryology.  The 
nervous  system  develops  from  a  broad  axial  stripe 
of  the  outer  germ-layer,  the  ectoderm,  that  imme- 
diately overlies  the  chorda  dorsalis  or  noto  cord. 
Within  this  stripe,  the  cells  of  the  outer  germ-layer 
grow  into  elongated  cylindrical  or  spindle-form  elements, 
while  those  within  the  adjoining  ectoderm  become  flat- 
tened. In  this  manner  the  outer  germ-byer  differ- 
entiates into  two  zones:  (i)  the  thinned  out  cuticle 
plate  and  (2)  the  thicker  axially  placed  neural  or 
medullary  plate. 

The  two  zones  soon  become  more  sharply  defined  from  each  other;  the  medullary 
plate  curves  ventrally  and  at  its  margins  rises  above  the  surface  of  the  gern..  In  this 
manner  arise  the  medullary  ridges,  which  include  between  them  the  broad,  and  at  first 
shallow,  medullary  groove.  The  ridges  are  simple  folds  of  the  outer  germ-layer,  along 
the  juncture  of  the  medullary  and  cuticle  plates. 

3 


ci^^-^»>C^^^ 


Medullary  ridge 


Medullary  tube 
(  entral  canal 


Fig.  r. — Schematic  representation  of  the 
formation  of  the  medullary  tube  from  the 
outer  germ-layer. 


4  MORPHOLOGY. 

The  medullary  plates  are  converted  into  the  medullary  tube  very  early.  This 
tube  is  formed  by  a  typical  folding  process.  The  medullary  ridges  progressively  rise 
above  the  dorsal  surface  of  the  embryo,  bend  medially  and  grow  towards  each  other 
until  their  summits  meet  and  later  fuse.  As  the  medullary  ridges  rise  above  the  surface 
of  the  embryonic  area,  they  draw  along  the  cuticle-plate ;  the  latter,  however,  does  not 
come  into  relation  with  the  nervous  system,  but  becomes  the  epithelial  covering  of  the 
body.  In  the  medullary  tube,  which  encloses  a  cleft-like  space,  the  central  canal  (^can- 
alis  centralis'),  filled  with  primary  lymph,  we  distinguish  the  brain-tube  and  the  spinal 
tube ;  from  the  former  develops  the  brain  and  from  the  latter  the  spinal  cord. 


Anterior  braht-vesic 
(  ProsencephaloK) 


Middle  bratii-v^sicl 
iMesencephnlon  ) 


Posterior  braiyi-'vesicle 
(Rhoijtbencephalon) 


^ _  Mid-brain 

'      ^^    _    V.  vesicle 


-Schematic  representation  of  the  three  primary  brain-vesicle: 


DEVELOPMENT   OF   THE    BRAIN. 

The  fundamental  form  is  the  simple  brain-tube.  In  consequence  of  increased 
growth  in  certain  parts  and  diminished  growth  in  others,  the  brain-tube  early  exhibits  a 
segmentation.       At  first  it    consists    of    three  dilatations,    the    primary    brain-vesicles, 

separated  by  two  annu- 
lar constrictions,  the 
vesicles  being  desig- 
nated as  anterior,  mid- 
dle and  posterior.  From 
these  three  brain-\'esi- 
cles  later  arise  the  three 
chief  divisions  :  the 
Fore-brain  or  Prosen- 
cephalon, the  Mid-brain 
or  Mesencephalon  and  the  Hind-brain  or  Rhombenceplialon.  The  three  primary  vesicles 
subsequently  give  rise  to  five  secondary  brain-vesicles,  since  the  fore-brain  differen- 
tiates into  the  telencephalon  and  the  die?icephalon,  while  the  hind-brain  divides  into 
the    tnetencephalon    and    the   myelen- 

tephalon.       The    hind-brain    is    sepa-  DienceHmion 

rated  from  the  mid-brain  bjr  a  narrow 
constricted  segment,  the  isthmus 
{isthmus  7'hombencephali) .  The  mye- 
lencephalon  is  continuous  with  the 
spinal  cord.  The  primitive  brain- 
tube,  therefore,  differentiates  into  six 
divisions  (Fig.  3)  :  the  telencephalon, 
the  diencephalon,  the  mesencephalon, 
the  isthmus,  the  metencephalon  and 
the  myelencephalon. 

In  the   later   stages,  the  devel- 
opment of   the  nervous   substance  is 

especially  vigorous  in  the  two  lateral  walls  of  the  neural  tube,  while  the  median  are  as  of 
its  floor  and  roof  (the  floor-  and  roof-plates')  for  the  most  part  remain  thin  and  epithelioid. 
The  different  divisions  of   the  brain-tube  participate  in  the    further    development    in    very 


Telencephalon 


Mesencephalon 


^leteitcephalon 


Myelencephalon 


Fig.  3. — The  five  secondary  brain-vesicles.      (His.) 


DEVELOPMENT   OF   BRAIN.  5 

unlike  degree.      Certain  segments  remain  far  behind,   while   others  far    outstrip  their  sur- 
roundings  in    consequence   of   their  vigorous    growth.      Along   with    the   displacement   of 


Telencephalon 


~y^—  —   —  I^Ietencephaloil 


—  —  -   -   ^tyelentepkalon 


certain  brain-segments  induced  by  unequal  growth,  other  processes  contribute  to  the  ef^ace- 
ment   of  the  original  fundamental  plan  of  the  whole.      Among  such  factors  belong  partic- 


embryo  of  the  third  month,     .\ftcr  a  model  by  His 


ularly  the  appearance  of    robust  cross-fibres  (corpus  callosum,    pons).      Consequently  it  is 
impossible  to  mark    off    superficially  the    individual    segments    on  the    brain  of    the  adult. 


6  MORPHOLOGY. 

The  developmental  relations  of  the  parts  of  the  brain  to  the  individual  brain-vesicles  is 
best  explained  by  the  accompanying  table  after  His.  It  will  serve  as  guide  in  the  con- 
sideration of  the  morphology.       (Compare  also  Figs.    5,   6,    7,   8,   9.) 


Telencefhalot. 


Corpus  striatum 
Rhlnettcephalott 


Fig.  6. — Diagram  showing  the  further  development  of   the  five 


The  prosencephalon  and    the    mesencephalon  together  are    also  designated  the  cere- 
brum or  great  brain.      The  brain-stem  {triaicus  cerebri)  embraces  the  so-called  the  brain- 


FlG.   7. — Median  sagittal  section  through  the  adult    brain.     Telencephalon    is  yellow;    diencephalon  red;    mesencephalon 
blue;  metencephalon  green;  myelencephalon  violet. 

ganglia;  it    consists    of    the    stem    of    the    end-brain,   the    inter-brain,   the  mid-brain,   the 
isthmus,   the  pons  and  the  medulla  oblongata. 


SUBDIVISIONS    OF  THE    BRAIN. 


Prosencephalon — Fore-Brain     < 


-i 


f  f  Pallium 

J    Hemisphaerium         \   Rhinencephalon 
I  L  Stem  of  End- Brain 

[    Pars  optica  Hypothalami 
Pars  mamillaris  Hypothalami 

f   Thalamus 
Thalamencephalon  j    Metathalamus 
[  [   Epithalamus 

Mesencephalon— Mid-Brain      / |    Pedunculi  cerebri 


Telencephalon 


Diencephalon 


I 


\ 


Corpora  quadrigemina 


I   Isthmus   rhombencephali 

Rhombencephalon— Hind-Brain  I       Metencephalon       .       ere  3e 

(    Pons 


Medulla  oblongata 


Fig.  g. — Median  saffittal  section   through  the  b 


MORPHOLOGY. 


?ntricnlare 
f  Monroi) 


The    cavities    of     the    embryonal    brain-vesicles    likewise    change    their    form    under 
the    influence    of    the    various    growth-processes.        The    central    canal    of   the    spinal  cord 

is  continued  into  the  hind-part  of 
the  myelencephalon.  The  cavity  of 
the  fore  -  part  of  the  myelencephalon 
and  that  of  the  entire  metencephalon 
become  the  fourth  ventricle.  The 
cavity  of  the  mid-brain  remains  as 
the  aquaeductus  cerebri  or  Sylvian 
aqueduct.  The  cavity  of  the  dien- 
cephalon  or  inter- brain  becomes  the 
third  ventricle,  which  communicates 
with  the  lateral  ventricles  —  the  cav- 
ities of  the  hemisphere  -  vesicles  —  by 
means  of  the  Y-like  foramen  of  Monro 
{^formnen  interventriculai'e') .  All  these 
spaces    are    filled   with   a  fluid,   the  liquor  cerebro-spinalis. 


DEVELOPMENT    OF    THE   SPINAL    CORD. 

The  part  of  the  neural  tube  that  becomes  the  spinal  cord  appears  of  oval  form  on 
transverse  section.  The  central  canal  forms  a  dorso-ventrally  directed  cleft,  which  is 
bounded  laterally  by  the  thickened  walls  of  the  medullary  tube,  but  dorsally  and  ven- 
trally  by  thinner  parts  of    the  same  ;    therefore,   a  separation   into  a  right  and  left  half  is 


Floor  fLatf 

Fig.   II. — Cross-section    of    spinal   cord  of  a 
human    embryo    of    four    and    one-half    weeks. 


Fig.   12. — Cross-section  of   spinal  cord  of  a  hu 
man  embryo  of  three  months.   (His.) 


easily  recognizable.  The  thinner  dorsal  and  ventral  walls  appear  as  commissures  behind 
and  before,  the  dorsal  or  posterior  commissure  being  called  the  roof-plate  and  the  ventral 
or  anterior  commissure  the  floor-plate.  During  the  further  development,  these  plates 
grow  relatively  little,  while  both  lateral  halves  continue  to  thicken,  their  growth  being 
especially  marked  ventrally.  In  this  locality  on  each  side  appears  a  ventral  projection. 
Consequently,  the  floor-plate  is  pushed  farther  from  the  surface  and,  finally,  a  median 
longitudinal    cleft,    the  fissura    mediana    anterior,   is  formed  in  front.       A  similar    change 


THE    SPINAL    CORD. 


occurs  in  the  dorsal  region,  the  roof-plate  being  likewise  pushed  in  and  disappearing 
at  the  bottom  of  the  sukus  medianus  posterior.  The  spinal  cord  now  consists  of  two 
robust  lateral  halves,  separated  from  each  other  by  an  anterior  fissure  and  a  posterior 
sulcus.  During  this  further  development  also  the  central  canal  has  changed  its  form, 
since  the  dorsal  part  of  the  original  dorso-ventrally  directed  cleft  becomes  closed  in 
consequence  of  the  apposition  of  the  lateral  walls. 

At  first  the  spinal  cord  extends  the  entire  length  of  the  vertebral  canal  with  a  fairly 
constant  volume.  The  lower  end  of  the  cord  becomes  rudimentary  and  defined  from 
the  preceding  part,  assumes  a  conical  form  and  becomes  the  conns  medullaris.  A  fur- 
ther alteration  in  the  extension  of  the  spinal  cord  is  brought 
about  by  the  inequality  between  its  growth  and  that  of  the 
surrounding  vertebral  canal.  The  latter  constantly  increases 
in  length,  the  lower  segment  of  the  spine  developing  with 
especial  vigor.  Since  the  growth  of  the  cord  fails  to  keep 
pace  with  that  of  the  spine,  the  cord  apparently  shortens 
and  no  longer  extends  the  entire  length  of  the  vertebral 
canal.  The  conus  medullaris  is  drawn  up  from  the  sacral 
canal  and  enters  the  lumbar  region,  untU,  finally,  it  is  found 
opposite  the  first  or  second  lumbar  vertebra.  During  this 
ascejistis  medullae  spinalis  the  end  of  the  conus  medullaris 
is  drawn  out  into  a  thin  thread,  which  extends  as  far  as  the 
coccygeal  region  and  is  known  as  the  fihan  terminale.  A 
further  consequence  of  this  ascensus  is  a  change  in  the 
course  of  the  nerves  emerging  from  the  spinal  cord.  In 
the  cervical  region  the  course  of  the  nerves  is  still  horizontal  ; 
in  the  thoracic  region  it  is  more  and  more  oblique  ;  while 
in  the  lumbar  region,  and,  still  more  in  the  sacral,  the  nerves 
are  directed  downward.  The  nerve-trunks  emerging  from 
the  last  part  of  the  cord  lie,  therefore,  for  a  long  distance 
within  the  vertebral  canal  before  they  leave  the  latter.  They 
surround  the  conus  medullaris  and  the  filum  terminale  and 

in  this  manner  lead  to  the  formation  of  the  so-called  horse-tail  or  cauda  equina.  In 
completion,  the  spinal  cord  undergoes  some  further  changes  in  its  form.  Gradually  two 
segments  acquire  greater  development,  the  one  in  the  cervical  portion  and  the  other  in 
the  upper  part  of  the  lumbar  region.  They  are  known  as  the  cervical  enlargement 
(intmnesceyitia  cervicalis)  and  the  lumbar  enlargement  {intiimesccntia  lumbalis)  respectively. 


FORM,    SIZE   AND    WEIGHT   OF   THE    BRAIN. 

The  brain  possesses  in  a  general  way  the  form  of  the  cranial  cavity.  It  is 
applied  so  closely  to  the  inner  wall  of  the  skull,  that  a  cast  of  the  cranial  cavity 
repeats  to  a  considerable  degree  the  form  of  the  brain.  Corresponding  to  the  numerous 
variations  in  the  configuration  of  the  skull,  sometimes  the  brain  is  more  spherical 
and  at  other  times  more  ellipsoidal  in  form.  Its  dorsal  surface  is  arched,  its  ventral 
one   flattened. 


lo  MORPHOLOGY. 

The  length  of  the  brain  is,  on  an  average,  between  160-170  mm.  and  its  greatest 
transverse  diameter  140  mm.  The  female  brain  is  usually  somewhat  shorter  than  the 
male.  The  weight  of  the  brain  has  long  been  the  subject  of  numerous  investigations. 
The  average  brain-weight  of  the  adult  man  has  been  found  to  be  1375  grams,  that  of 
the  adult  woman  1245  grams.  The  minimal  weight  of  the  male  brain  has  been  placed 
at  960  grams,  that  of  the  female  brain  at  800  grams.  As  maximal  weights,  2000 
grams  and  over,    1900  grams,    1861  grams  and  1807  grams  have  been  specified. 

The  difficulty  of  determining  the  average  brain-weight  lies  in  the  fact  that  various 
factors  exert  a  substantial  influence.  In  this  connection  age  plays  a  prominent  role. 
Observations  show  that  the  mean  brain-weight  in  both  sexes  reaches  its  maximum 
towards  the  twentieth  year,  remains  stationary  between  the  twentieth  and  fiftieth  years, 
and  then  gradually  decreases.  Further  influences  are  body-weight  and  body-length.  In 
general,  heavier  individuals  possess  a  heavier  brain  and  with  increase  in  height  is  asso- 
ciated increase  in  brain-weight  ;  small  individuals,  however,  possess  a  relatively  heavier 
brain  than  large  ones.  In  relation  to  the  form  of  the  skull,  a  higher  average  brain- 
weight  has  been  found  in  the  broad-headed  type  than  in  the  long-headed.  Many  obser- 
vations regarding  the  influence  of  race  e.xist,    with  the  following  results  : 

Grams. 

Caucasian  race:  average  brain-weight,  1335 

Chinese:  average  brain-weight,  1332 

Sandwich  Islander:  average  brain-weight,  1303 

Malay  and  Indian:  average  brain-weight,  1266 

Negro:  average  brain-weight,  1244 

Australian:  average  brain-weight,  1185 

Definite  differences  in  the  brain-weight  among  the  European  nations  have  been 
recorded : 

Grams. 

German  :  average  brain-weight,  1425 
EngUsh :  average  brain-weight,  1346 
French  :     average    brain- weight,    1280 

Among  all  peoples,   the  female  sex  shows  a  smaller  average  brain-weight. 

Further,  the  influence  of  culture  is  to  be  noted.  According  to  the  measurements 
of  P.  Broca,  among  the  cultured  nations  the  brain-mass  probably  gains  somewhat  in  the 
course  of  time.  Based,  on  the  measurements  of  Egyptian  skulls,  E.  Schmidt  found  that 
nations,  which  have  regressed  from  a  higher  culture,  exhibit  a  smaller  cranial  capacity 
than  that  possessed  by  them  during  the  period  of  their  cultural  bloom. 

Finally,  pathological  conditions  must  also  be  considered,  since  sometimes  they  in- 
duce an  increase  and  at  other  times  a  decrease  of  the  brain-weight. 

Of  great  interest  has  always  been  the  question,  to  what  extent  do  the  absolute  and 
relative  proportions  of  the  brain  indicate  the  favored  position  which  man  enjoys  in  com- 
parison with  other  animals.  It  has  long  been  known,  that  man  does  not  possess  abso- 
lutely the  heaviest  brain.  The  brain-weight  of  the  elephant  reaches  4000  grams  and 
more,   while    that  of   certain  cetaceans  may  be  3000  grams.        It    is,   however,   clear  that, 


BRAIN-WEIGHT.  ii 

in  proportion  to  body-weight,  these  animals  possess  relatively  a  smaller  brain-mass  than 
does  man.  On  the  other  hand,  several  investigators  have  shown  that  man  does  not 
possess  relatively  the  heaviest  brain,  since  in  this  respect  he  is  surpassed  by  certain  song- 
birds, apes  and  mice.  If,  however,  one  compares,  as  did  Ranke,  the  weight  of  the 
spinal  cord  with  that  of  the  brain,  man  is  found  to  possess  the  heaviest  brain.  While 
this  proportion  in  the  adult  human  subject  is  approximately  2  per  cent,  in  the  anthro- 
poid apes  this  ratio  increases  to  about  6  per  cent.,  and  among  the  other  mammals  it 
rises  to  from  23  to  47  per  cent. 

It  is  particularly  difficult  to  establish  a  definite  relation  between  brain-weight  and 
intelligence.  The  comparison  of  many  brains  shows,  that  it  is  not  permissible  to  esti- 
mate the  intellectual  capacity  of  an  individual  merely  according  to  his  brain-weight.  The 
following  data  exist  regarding  the  weights  of  the  brains  of  distinguished  men: 


Grams. 

Grams. 

Turgenjeff : 

2012 

Broca : 

1484 

Cuvier : 

1861 

Dupuytren  : 

1437 

Byron : 

1807 

Dante  : 

1420 

Kant  : 

1600 

Liebig  ; 

1352 

Schiller  : 

1580 

Tiedemann  : 

1254 

Gauss : 

1492 

Dollinger: 

1207 

This  comparison  shows,  that  while  the  majority  of  these  brains  exceeded  the 
average  weight  of  1375  grams,  there  are  also  men  of  eminent  intellect  who  possess  a 
relatively  low  brain-weight.  Moreover,  there  are  records  of  notable  brain-weights  (2028 
and  1900  grams)  among  individuals  of  insignificant  mentality.  Remarkably  low  brain- 
weights  (300  grams  and  less)   occur  among  idiots. 

According  to  the  present  investigations,  the  conclusion  is  justified,  that  psychic 
functions  can  proceed  normally  only  where  the  brain-weight  has  passed  a  certain  mini- 
mum. According  to  Obersteiner,  the  lowest  level  to  which  the  brain-weight  may  sink 
without  noticeable  impairment  of  the  intellectual  faculties  is  for  the  male  brain  1000 
grams  and  for  the  female  900. 

It  is  to  be  noted,  that  weighing  the  entire  brain  supplies  only  an  uncertain  index 
of  the  psychic  capability,  for  the  reason  that  the  individual  parts  of  the  brain,  so  varying 
in  structure  and  function,  do  not  undergo  uniform  increase  or  diminution  in  size  and 
weight.  An  accurate  knowledge  of  the  weights  of  the  individual  parts  of  the  brain 
would  be  of  great  importance,  especially  an  exact  determination  of  the  weight  of  the 
gray  substance  of  the  end-brain,  the  cerebral  cortex,  with  which  particularly  the  higher 
jjsychic  functions  are  associated.  Even  then  we  would  fail  to  reach  a  positive  result, 
since,  in  addition  to  the  weight,  other  relations  must  be  considered,  especially  the  finer 
structure. 

GENERAL  INSPECTION  OF  THE  BRAIN. 

Let  us  first  examine  the  dorsal  surface  of  the  brain.  This  is  strongly  arched  in 
the  sagittal  as  well  as  in  the  frontal  direction— /acies  cotivexa  cerebri  (Fig.  14).  A 
deep    median    vertical   cleft  (fissiira   longitudhialis    cerebri)    divides   the   whole   into    two 


MORPHOLOGY. 


Fisslira  longihidlnalis  cerebri 


symmetrical  halves,   the  hemispheres  of  the  end-brain.      On  probing  to  the  bottom  of  the 
fissure,   one    learns  that    the    separation  is  not    complete,   since  in  the  middle  of  the    cleft 

the  two  halves  are  united  by  a  broad  hori- 
zontal commissure,  the  corpus  callosuin.  In 
front  of  the  latter,  the  fissure  passes  to  the 
ventral  surface  of  the  brain ;  behind  the 
commissure,  the  fissure  likewise  penetrates 
deeply  and  ends  in  a  large  transverse  cleft 
(fissura  transversa  cerebri),  which  separates 
the  hemispheres  from  the  subjacent  cere- 
bellum. The  surface  of  the  hemispheres  ex- 
hibits clefts  and  furrows  of  varying  depths 
and  the  intervening  convolutions. 

The  ventral  surface  of  the  brain,  known 
as  the  basis  cerebri,  is  much  more  com- 
plexly modelled.  In  the  first  place,  we  per- 
ceive to  what  extent  the  hemispheres  occupy 
also  the  base  of  the  brain.  In  the  anterior 
part,  the  fissura  longitudinalis  cerebri  runs 
in  the  mid-line,  as  far  backward  as  an  X- 
frontai  pole  below,   shaped    Structure,    the     chiasma    opiicum.       On 


Fissura  longltudijialis  cerebr 


Tract,  otfact 


j,„.,o..,,.       Medulla       Sulc. 
cerebelti  post      oblongata     literal,  ant 


Diagonal  band 


N.  optic 


Fossa  ititer- 
peditncitlaris 
(Snbst.  per  J. 
post) 

Pons  and  Sulc. 

basilaris  pontis 


N.  hypoglossits 


Fig.   is. — Basal  aspect  of  the  brain. 


BASAL  ASPECT  OF  BRAIN.  13 

folding  the  chiasma  slightly  backward,  one  sees  a  thin  gray  and  easily  torn  lamella 
stretching  from  the  front  border  of  the  chiasma  into  the  depth  of  the  hssura  longitudi- 
nalis  cerebri  ;  this  is  the  lamina  terminalis.  Forwards  from  the  chiasma  lead  the  nerves 
of  sight  {iiervi  opHci),  while  posteriorly  and  laterally,  on  each  side,  extends  the  visual 
path,  the  tradus  optici.  Lateral  from  the  chiasma  and  the  optic  tract  lies  a  gray  field, 
penetrated  by  larger  and  smaller  openings,  the  substantia  perforata  anterior.  The 
anterior  boundary  of  this  field  presents  a  triangular  area,  the  trigonum  olfactorium,  from 
whose  front  point  a  narrow  white-stripe,  the  tractiis  olfactorius,  leads  forward  to  end  in 
the  broadened  terminal  bulbus  olfactorius.  The  olfactory  nerve-fibres  {fila  olfactoria) 
extend  from  the  ventral  surface  of  the  bulb  as  delicate  white  thread-like  strands,  that 
have  been  torn  in  removing  the  brain.  Bulbus  olfactorius,  tractus  olfactorius,  trigonum 
olfactorium,  substantia  perforata  anterior  are  all  parts  of  the  rhinencephalon.  These  will 
be  more  closely  considered  in  connection  with  the  rhinencephalon. 

Behind  the  chiasma  opticum  rises  a  gray  hump,  the  tuber  ciiiereum,  that  tapers  to 
the  infundibulum  bearing  a  bean-shaped  gray  body,  the  hypophysis  or  pituitary  body. 
The  hypophysis  lies  in  the  sella  turcica  of  the  body  of  the  sphenoid  and  may  readily 
become  separated  in  consequence  of  the  tearing  of  the  thin  infundibulum,  when  the 
brain  is  taken  out,  so  that  only  the  conical  pointed  part  of  the  infundibulum  presents, 
while  the  hypophysis  remains  within  the  sella  turcica.  Laterally,  the  tuber  cine- 
reum  is  bounded  by  the  tractus  optici,  whose  further  course  is  over  the  forward  and 
outwardly  coursing  cerebral  stalks,  the  pedimculi  cerebri,  and  then  to  pass  deeply. 
Behind  the  tuber  cinereum,  rise  two  white  pyriform  structures,  the  corpora  mamil- 
laria  or  cajidicantia.  Behind  these  and  between  the  pedunculi  cerebri  lies  the  fossa 
interpeduncularis,  which  is  prolonged  backward  into  the  recessus  posterior  and  forward 
into  the  recessus  anterior.  The  floor  of  this  depression  is  formed  by  the  substantia 
perforata  posterior,  a  gray  surface  modelled  by  numerous  apertures  and  divided  into 
halves  by  a  median  furrow.  Towards  the  cerebral  peduncle  it  is  bounded  by  a 
groove,  the  sulcus  nervi  oculomotorii,  from  which  emerge  the  fibres  of  the  oculo- 
motor nerve. 

Behind  these  deeply  sunken  structures,  appears  a  white,  broad,  transverse  bridge, 
the  pons  Varolii,  which  in  front  and  behind  is  sharply  bounded,  in  the  middle  is  impressed 
by  a  broad  median  furrow,  the  sulcus  basilaris,  and  at  the  sides  narrows  and  then  extends 
laterally  and  backward  to  sink  into  the  cerebellum.  Behind  the  pons  lies  the  tapering 
bulb,  the  medulla  oblongata,  which  is  prolonged  into  the  spinal  cord.  It  presents  the 
median  longitudinal  furrow,  the  fssura  mediana  anterior,  that  is  bounded  on  each  side 
by  a  white  strand,  the  pyramid  or  pyramis.  Beyond  the  pyramidal  tract,  the  sulcus 
lateralis  anterior  extends  as  a  shallow  groove,  beyond  which,  in  turn,  lies  an  elongated 
egg-shaped  elevation,  the  oliva  or  olivary  eminence.  The  medulla  covers  the  median 
part  of  the  cerebellum,  occupying  a  broad  furrow,  known  as  the  vallecula  cerebelli, 
behind  which  appears  the  strongly  arched  ventral  surface  of  the  cerebellum.  A  deep 
median  cleft,  the  incisura  cerebelli  posterior,  separates  the  two  halves  of  the  little  brain,  the 
hemisphaeria  cerebelli,  which  exhibit  numerous,  more  or  less  parallel  narrow  tracts,  the 
folia.  On  slightly  raising  the  cerebellum,  the  fssura  transversa  cerebri  appears  as  a 
deep  cross  cleft,  separating  the  cerebellum  from  the  cerebrum  and  opening  into  lh&  fissura 
longitudinalis  cerebri. 


H 


MORPHOLOGY. 


Closer  examination  of  the  base  of  the  brain  leads  further  to  the  location  of  the 
exits  of  the  individual  cerebral  nerves  from  the  brain,  concerning  which  the  following 
table  may  afford  explanation.      The  exits  of  these  nerves  from  the   skull   are   also    noted. 


Nerve 

Exit  from  the  Brain 

E.xit  from  Skull. 

I. 

Fila  olfactoria 

Bulbus  olfactorius 

Lamina  cribrosa 

II. 

N.  opticus 

Chiasma  opticum 

Foramen  opticum 

III. 

N.  oculomotoris 

Sulcus  nervi  oculomotorii,  close  in  front 
of  pons,  on  medial   edge  of  cerebral 
peduncle 

Fissura  orbitalis  superior 

IV.     N.  trochlearis 


V.     N.  trigeminus 


VI.     N.  abducens 


VII.     N.  facialis 


VIII.     N.  acusticus 

IX.     N.  glosso- 

pharyngeus 

X.     N.  vagus 
Xi.     N.  accessorius 


XII.     N.  hypoglossus 


Dorsal,  behind  the  corp.  quadrigemina, 
lateral  to  frenulum  veil  medullaris  an- 
terioris.  Course  around  the  cerebral 
peduncle 

Front  border  of  pons,  lateral,  near  the 
entrance  of  middle  cerebellar  peduncle 
into  the  cerebellum 

Hind  border  of  pons,  in  the  groove 
between  the  latter  and  the  medulla 
(pyramid) 

Lateral  to  N.  abducens,  on  hind  border 
of  pons,  in  front  of  and  lateral  to  olive 


Lateral  to  N.  facialis,  on  hind  border  of 
pons,  lateral  to  olive 

Behind  the  N.  facialis  and  N.  acusticus, 
in  upper  part  of  furrow  behind  olive 

Behind  the  N.  glossopharyngeus,  in  the 
furrow  behind  the  olive 

Upper  root -fibres  (cerebral  portion): 
behind  N.  vagus,  in  the  furrow  behind 
the  olive 

Lower  root-fibres  (spinal  portion)  :  be- 
tween the  front  and  hind  roots  of  the 
cervical  nerves,  aS  far  as  5th  or  6th. 

Sulcus  lateralis  anterior,  between  pyra- 
mid and  olive 


Fissura  orbitalis  superior 


R.  ophthalmicus:  Fis.  orbit,  sup. 
R.  maxillaris:  Foram.  rotundum 
R.  mandibularis:  Foram.  ovale 

Fissura  orbitalis  superior 


Porus  acusticus  internus— 
Meatus  acusticus  internus — 
Canalis  facialis 
Foramen  stylo-mastoideum 
Porus  acusticus 


Foramen  jugulare 
Foramen  jugulare 
Foramen  jugulare 


Canalis  hypoglossi 


N.  I,  II  and  VIII  are  sensory  nerves, 

N.  V,  VII,  IX  and  X  are  mixed  nerves, 

N.  Ill,  IV,  VI,  XI  and  XII  are  motor  nerves. 


Let  us  now  examine  a  median  sagittal  section  through  the  brain.  In  the  first 
place,  we  recognize  the  brain-mass  belonging  to  the  hemisphere,  with  its  fissures  and 
convolutions,    and,    further,     the    corpus    callosum,   the    large    commissure    connecting    the 


CORPUS   CALLOSUM. 


15 


two  cerebral  hemispheres.  The  middle  part  of  the  bridge  is  the  body  {truncus  corporis 
callosi);  behind,  the  commissure  thickens  to  form  the  spleniutn;  while  in  front,  it  bends 
sharply  downward  and  forms  the  knee,  gemc  corporis  callosi,  that  tapers  into  the  beak- 
like rosiriivi  corporis  callosi.       The  latter  is  prolonged  as  a  short  thin  white  lamella,   the 


Corpus  cnllosnm   (Trtninis) 

Sept.  pelluddnm^ 
Corpus  callosum  {Genu) 


Medulla  oblongata 


Fig.    16. — Median  sagittal  sectic 


Fic.  17. — Median  sagittal  eection  '.hrough  the  adult  brain. 


lamina  roslralis,  which  is  continuous  with  the  attenuated  lamina  terminalis  that  cxicnds 
to  the  front  surface  of  the  chiasma  opticum.  Behind  the  corpus  c:i!!osum,  covered  by 
the  hinder  part  of  the  hemisphere,  lies  the  cerebellum  ;  the  deep  (issura  transversa 
cerebri  is  plainly  seen  separating  the  hemisphere  and  cerel)ellum. 


i6 


MORPHOLOGY. 


Let  us  examine  the  parts  of  the  brain  lying  beneath  the  corpus  callosum.  Closely 
attached  to  the  under  surface  of  the  latter,  a  lamella  of  white  matter  extends  forward 
from  the  place  where  the  splenium  joins  the  body  or  trunk  of  the  corpus  callosum.  The 
structure  gradually  leaves  the  corpus  callosum,  arches  downward  with  forwardly  directed 
curve  until  close  behind  the  lamina  rostralis,  and  then  sinks  deeply  into  the  brain-sub- 
stance, just  behind  a  transversely  cut  white  bundle  of  fibres,  the  anterior  commissure  or 
commissura  anterior.  This  white  lamella  belongs  to  the  fornix.  Between  the  fornix, 
on  the  one  hand,  and  the  truncus,  genu,  rostrum  and  lamina  rostralis  of  the  corpus 
callosum,  on  the  other,   extends  a  thin  white  sheet,   the  septum  pellucidum.      Beneath  the 

Fornix  Foraineti  AIo7irot 


Commissura  anterior 


Gyms  cingidt 


Cyrus  subcallosns  '  —  ^^^ 


Area  parolfactoria. 
(.Br oca's  field) 


Massa  ijiiertnedia 


Commissura  hate- 


FlG.  i8. — Median  sagittal  section  through  the  adult  brain;  subcallosal  region. 


fornix  and  the  hind  part  of  the  corpus  callosum  is  situated  the  thalamus.,  between  whose 
fore-end  and  the  descending  fornix  lies  an  opening,  the  foramen  interventriculare  or  foramen 
of  Monro.  At  the  posterior  end  of  the  thalamus,  beneath  the  splenium  corporis  callosi, 
lies  the  pineal  body,  the  corpus  pineale.  The  cleft,  which  penetrates  the  pineal  body  in 
front,  is  called  the  recessus  pinealis.  Immediately  beneath  is  found  the  cross-section  of 
the  commissura  posterior  ce7'ebri,  with  which  are  joined,  proceeding  backward,  the  lamijia 
qiiadrigemina,  the  vehtm  medullare  aiiterius  and  the  cerebellum.  On  the  median  surface 
of  the  thalamus,  behind  the  foramen  interventriculare,  lies  the  cross-section  of  the  middle 
commissure  or  massa  intermedia,  by  means  of  which  the  opposed  surfaces  of  the  two 
thalami  are  connected. 

The  sulcus  hypothalamicus   {Monroi')    is  a  furrow  that  extends  backward  from    the 
foramen  interventriculare,  beneath  the  massa  intermedia,  towards  the  commissura  posterior 


TELENCEPHALON.  17 

and  separates  the  region  of  the  thalamus  from  the  more  dependent  hypothalamus.  On 
examining  this  region  more  closely,  we  note  again  parts  that  have  been  mentioned  in 
connection  with  the  base  of  the  brain  :  in  front  the  latniiia  iermma/is  that  joins  the 
anterioi  surface  of  the  chiasma  oplicum,  the  recessus  opticus  between  the  lamina  and  the 
chiasma  and  behind  the  latter,  the  recessus  infundibuH,  the  inftindibulum  with  the  hypoph- 
ysis, the  tuber  cinereuTn,  the  corpus  mamillare,  and  the  substantia  perforata  posterior, 
forming  the  floor  of  Xh^  fossa  iyiterpeduncularis  {Tarini). 

Continuing  backward,  the  cerebral  peduncle,  the  pons  and  the  medulla  oblongata 
are  seen  in  cross-section.  The  sulcus  hypothalamicus,  running  backward  from  the 
foramen  interventriculare,  opens  into  the  aquaediutus  cerebri,  or  aqueduct  of  Sylvius, 
which  extends  beneath  the  quadrigeminal  plate  and  joins  the  fourth  ventricle  that  under- 
lies the  cerebellum   (Figs.    16,    17,   and   18). 

TELENCEPHALON. 

The  telencephalon  or  end-brain  includes : 
The  hemisphaerium, 
The  pars  optica  hypothalami. 
To  the  hemisphaerium  belong : 

The  pallium  or  cerebral  mantle, 
The  rhinencephalon, 

The  stem  of  the  telencephalon — the  gray  nuclei  of   the  end-brain. 
To  the  pars  optica  hypothalami  belong ; 
The  lamina  terminalis, 
The  chiasma  opticum. 
The  tuber  cinereum, 
The  infundibulum, 
The  hypophysis. 
The  hemisphaerium  contributes  the  chief  mass  of  the  end-brain. 

In  order  to  study  the  morphology  of  the  telencephalon  to  the  best  advantage,  one 
proceeds  in  the  following  manner :  the  brain  is  placed  on  the  dorsal  surface,  with  the 
base  upward  ;  the  pons,  cerebellum  and  medulla  oblongata,  all  connected,  are  completely 
separated  from  the  brain  by  a  transverse  cut  passing  through  the  front  border  of  the 
pons.  A  second  cut,  sagittal  and  in  the  mid-line,  divides  the  two  hemispheres  from 
each  other. 

In  the  first  place,  let  us  e.xamine  a  hemisphere  in  general.  Each  hemisphere 
presents  three  surfaces  :  a  convexly  arched  dorso-lateral  surface,  a  flat  median  surface, 
and  a  basal  surfaee,  which  is  subdivided  by  a  deep  incision  into  a  smaller  anterior  and 
a  larger  posterior  part.  We  distinguish  further  an  anterior  frontal  pole  {polus  frontalis), 
a  posterior  pole  {polus  occipitalis)  and  a  temporal  pole  {polus  temporalis),  the  latter 
representing  the  fore-end  of  the  posterior  division  of  the  basal  surface.  A  dorsal  border 
marks  the  transition  of  the  lateral  to  the  median  surface  ;  its  medial  continuation  forms 
the  base  to  the  basal  border.  The  lateral  border  corresponds  to  the  transition  of  tlie 
lateral  at  the  basal  surface. 


i8 


MORPHOLOGY. 


PALLIUM— CEREBRAL  MANTLE. 

The  surface  of  the  palHum  or  cerebral  mantle  is  subdivided  into  definite  lobes  {lobi) 
by  definite  and  usually  deep  clefts  and  furrows,  the  Jissures  and  sulci.  Of  such  di\'isions 
or  lobi  cerebri  are  recognized  : — 

Lobus  frontalis, 

Lobus  parietalis, 

Lobus  temporalis, 

Lobus  occipitalis. 

An  additional  special  lobe,  the  insula  or  island  of  Reil,  lies  hidden  at  the  bottom 
of  the  lateral  or  Sylvian  fissure.  Each  lobe  further  exhibits  convolutions  {gyri  cerebri"), 
which,   while  bounded  by  the  fissures,   are  often  connected  at  the    bottom  of    the  fissures 


Sulc.  froniaL      S71IC.  front.  'Sulc,  ^rae-     Side,  cettiralis     SitU.  post- 

jned.  sup.  central,  sup,         iRoiandi)  centralis    Sulc.  interpariet. 


SuU.  prnecentral. 
inf. 

Sulc.  front'tl.    inf. 

Sulc.  radiai. 

Polus  frontalis 

Ra7n,  ant.  ascend. 
Ram.  ant.  Jioin- 

Rain.  ant. 
Tntncus  fissurae 

Fissiira  cerebri    Poliis  tem-    Sulc.  temp,        Sulc.        Sitlc.  /ncisitra  praeoccipitttl. 

lateral.   (Ram.  post.)        poralis  siip.  teinp.ined.   teinp.inf. 


Sulc.   internted. 

Fissnra  parieto 

occipit. 
Sulc.  Intemied. 

sectind, 
Sulc    orcipit. 
transver^. 


superi 

Polus  occipitalis 


Fig. 


-Do 


D-lateral  cerebral  surface.     Fissures  and  convolutions. 


by  deep  convolutions  {gyri  profundi).  The  short  superficial  or  sunken  convolutions 
that  connect  two  longer  gyri  are  called  annectant  convolutions  (^gyri  transitivi).  The 
secondary  fissures  {incisura)  are  superficial  aberrant  furrows,  usually  uncertain  in  their 
course  and  springing  from  deeper  sulci,  that  cut  into  the  convolutions  and  in  certain 
cases  cause  doubling  of  the  gyri. 


LOBES  AND  GYRI  OF  THE  DORSOLATERAL  SURFACE. 

Turning  again  to  the  basal  aspect  of  the  hemisphere,  the  vallecula  Sylvii  {fossa 
cerebri  lateralis)  appears  as  a  deep  cleft,  lateral  to  the  substantia  perforata  anterior,  that 
separates  the  basis  cerebri  into  an  anterior  and  posterior  division.  From  the  valley  the 
ftssura  cerebri  lateralis,  or  Sylviari  fissure,  extends  outward,  at  first  as  the  truncus  fissurae 
lateralis,  toward  the  dorso-lateral  surface  of  the  hemisphere.  On  reaching  the  latter,  the 
fissure  divides  into  three  branches  :  ( i )  the  short  ramus  anterior  horizontalis ,  running 
horizontally  forward,  (2)  the  ramus  anterior  ascendens,  also  short  and  directed  almost 
vertically  upward,  and   (3)  the  long  ramus  posterior,  which  continues  the  direction  of  the 


FISSURES    AND    CONVOLUTIONS.  19 

anterior  horizontal  limb  backward  and  somewhat  obliquely  upward  and  at  its  end  usually 
divides  in  a  Y-like  manner  into  a  ramus  ascendeiis  and  a  ramus  descendens.  Approxi- 
mately from  the  middle  of  the  dorsal  border  of  the  hemisphere,  the  sulcus  centralis  or 
fissure  of  Roland,  runs  obliquely  downward  and  forward  toward  the  posterior  ramus  of 
the  fissura  cerebri  lateralis.  As  a  rule,  this  furrow  exhibits  two  knee-like  bends,  one  at 
the  junction  of  the  upper  and  middle  thirds,  the  other  at  the  transition  of  the  second 
and  lower  thirds  ;  the  fissure,  moreover,  usually  crosses  the  upper  border  of  the 
hemisphere.  4 

Lobus  frontalis.  The  frontal  lobe  lies  above  the  fissure  cerebri  lateralis  and  in 
front  of  the  central  fissure,  and  presents  the  following  fissures  and  convolutions.  The 
sulcus  praecentralis  superior  begins  somewhat  below  the  upper  border  of  the  hemisphere 
and  runs  more  or  less  parallel  with  the  sulcus  centralis.  Somewhat  lower,  the  sulcus 
praecentralis  inferior  continues  in  the  same  direction  and  below  penetrates  between  the 
ramus  anterior  ascendens  fissurae  cerebri  lateralis  and  the  lower  end  of  the  sulcus  cen- 
tralis. The  upper  end  of  the  inferior  precentral  sulcus  almost  constantly  lies  in  advance 
of  the  lower  end  of  the  superior  fissure.  As  variations,  the  precentral  fissures  ma.Y  con- 
nect with  the  central  fissure  and  the  lower  precentral  may  join  the  fissura  cerebri  lateralis. 

The  sulcus  frontalis  superior  extends  forward  from  the  superior  precentral  sulcus, 
approaching  the  upper  border  of  the  hemisphere  in  front.  At  times  the  fissure  cuts 
through  the  sulcus  praecentralis  superior  towards  the  central  fissure,  thereby  producing 
the  cruciform  type  of  precentral  furrow.  In  many  cases  the  superior  frontal  sulcus  is 
interrupted    by  two  or   three   annectant    convolutions.     The  fissure  may  also  be  doubled. 

The  sulcus  frontalis  inferior  likewise  extends  forward,  from  the  inferior  precentral 
fissure,  but  more  arched  and  downward.  The  fissure  is  usually  clearly  marked,  but  it  may 
present  very  variable  forms  and  be  interrupted  by  deep  or  superficial  annectant  convolutions. 
Ordinarily  a  short  furrow,  the  sulcus  radiatus,  extends  downward  from  the  inferior 
frontal  between  the  anterior  horizontal  and  ascending  rami  of  the  fissura  cerebri  lateralis. 

The  small  sulcus  frontalis  medius  is  generally  to  be  seen  between  the  superior 
and  inferior  frontal  fissures.  This  sulcus  is  often  readily  identified,  but  it  may  exhibit 
the  most  diverse  forms,  since  it  may  be  displaced  or  effaced  by  annectant  con\^olutions. 
At  times  the  fissure  is  clearly  recognizable  as  a  continuous  and  deep  furrow. 

The  foregoing  fissures  bound  the  following  convolutions.  The  gyrus  centralis 
anterior  lies  between  the  superior  and  inferior  precental  fissures  in  front  and  the  central 
fissure  behind.  The  gyrus  frontalis  superior  is  bounded  by  the  superior  frontal  fissure 
below  and  the  superior  prefrontal  fissure  behind.  Between  the  superior  and  inferior 
frontal  fissures  extends  the  gyrus  frontalis  medius,  which  is  subdivided  by  the  median 
frontal  sulcus  into  a  pars  superior  and  a  pars  inferior.  The  gyrus  frontalis  inferior  lies 
below  the  inferior  frontal  fissure.  This  convolution,  also  known  as  Broca  s  convolution 
on  the  left  side,  includes  three  subdivisions: — 

The  pars  opercularis,  between  the  lower  end  of  the  inferior  precentral  fissure  and 
the  anterior  ascending  ramus  of  the  fissura  cerebri  lateralis; 

The  pars  triangularis,  between  the  anterior  ascending  and  horizontal  rami  of  rhe 
lateral  fissure ;  and 

The  pars  orbitalis,  between  the  anterior  horizontal  ramus  and  the  trunk  of  ihe 
lateral  fissure. 


20  MORPHOLOGY. 

Behind  the  sulcus  centrahs,  or  fissure  of  Rolando,  and  above  the  ramus  posterior 
of  the  fissure  of  Sylvius,  stretches  the  parietal  lobe,  while  below  the  last  named  fissure 
lies  the  temporal  lobe.  Posteriorly,  both  lobes  pass  into  the  occipital  lobe  without  a 
definite  boundary.  As  a  conventional  boundary,  we  may  adopt  a  line  that  unites  the 
dorsal  end  of  the  parieto-occipital  fissure,  which  incises  the  upper  border  of  the  hemi- 
sphere, with  the  incisura  praeoccipitalis.  The  Jissura  parieto-occipitalis  is  a  deep  cleft  on 
the  hind  part  of  the  median  surface  of  the  hemisphere  (Fig.  22),  which  incises  the  upper 
border  of  the  hemisphere  and  extends  a  short  distance  on  its  dorso-lateral  aspect.  It 
is  readily  identified  as  a  deep  incision  on  the  upper  border  of  the  hemisphere  about 
midway  between  the  central  fissure  and  the  occipital  pole,  rather  nearer  the  latter.  The 
incisicra  praeoccipitalis  appears  as  a  slight  notch  on  the  lateral  border  of  the  hemisphere, 
approximately  at  the  junction  of  the  middle  and  posterior  thirds  (Fig.    19). 

Lobus  parietalis.  The  sulcus  postcentralis  extends  behind  and  more  or  less 
parallel  with    the    central  fissure.       This  furrow  is     sometimes   continuous,   and    sometimes 


Gyr.  fronhiUs  supi 
Gyr.  frontalis  niediits 


Lobiihis  pfirieialis 


Gyr.  temporalis      Gyr.  temp.      Gyr.  temporalis  infei 
superior  Tnedius 


Fig.  20. — Dorso-lateral  cerebral  surface.     F: 


subdivided  into  two  parts,  the  sulcus  postcentralis  superior  and  inferior.  Each  sub- 
division may  retain  its  individuality,  or  at  the  same  time  join  the  sulcus  interparictalis. 
When  the  superior  postcentral  fissure  is  independent,  it  usually  exhibits  variations  in 
form  and  size,  sometimes  being  unbranched  and  paralleling  the  central  fissure,  but  often 
forming  a  three-  or  four-limbed  furrow.  As  does  the  precentral,  so  the  postcentral  fissure 
at  times  anastomoses  with  the  central  fissure ;  the  inferior  postcentral  fissure,  moreover, 
may  connect  with  the  Sylvian  fissure. 

The  sulcus  interparictalis  begins,  mostly  with  a  bifurcation,  behind  the  upper  end 
of  the  inferior  postparietal  fissure.  By  the  junction  of  this  sulcus  with  one  or  other  of 
the  postcentral  fissures,  a  veritable  vortex  of  furrows,  a  fissure-star,  is  formed.  The 
sulcus  interparictalis  pursues  an  arched  course  backward,  beneath  the  dorso-lateral  end  of 
the  parieto-occipital  fissure,  and  usually  opens  out  into  the  sulcus  occipitalis  tratisversics. 
Occasionally  the  interparietal  fissure  passes  across  the  transverse  occipital  furrow  and 
continues  backward  as  the  sulcus  occipitalis  superior.  The  interparietal  fissure  is  often 
made    up  of   several    parts  ;  during   its    course  isolated    fissures   are   given    off   upward  as 


FISSURES    AND    CONVOLUTIONS.  21 

well  as  downward.  .\  short  furrow,  known  as  the  sulcus  parietalis  transvcrsus  (Bris- 
saud),  extends  up^vard,  towards  the  border  of  the  hemisphere,  from  in  front  of  the 
dorsal  end  of  the  parieto-occipital  fissure.  Often  two  furrows  pass  downward.  One 
sulcus  runs  behind  the  ascending  end-branch  of  the  ramus  posterior  of  the  -Sylvian 
fissure  and  is  called  the  sulcus  intcrniedius  primus  (Jensen).  It  often  extends  as  a 
continuation  of  the  upper  transverse  parietal  fissure,  but  may  be  strongly  developed  and, 
indeed,  may  establish  a  connection  between  the  interparietal  fissure  and  the  ascending 
end  of  the  superior  temporal  fissure.  The  other  sulcus  is  given  off  farther  backward, 
runs  behind  the  ascending  end  of  the  superior  temporal  fissure  and  is  known  as  the 
sulcus  intermedius  sccundus  ( Eberstaller).  Both  of  these  sulci  intermedii  may  also  exist 
as  independent  fissures. 

By  means  of  the  foregoing  fissures  the  following  convolutions  are  defined  :  the 
gyrus  centralis  posterior  lies  behind  the  sulcus  centralis,  bounded  below  by  the  fissura 
cerebri  lateralis  and  behind  by  the  fissura  postcentralis.  Above  the  sulcus  interpari- 
etalis  lies  the  lobulus  parietalis  superior,  while  beneath  this  fissure  extends  the  lobulus 
parietalis  inferior.  This  lower  parietal  lobule  presents  two  special  convolutions,  the 
gyrus  supramarginalis  and  the  gyrus  angularis.  The  gyrus  supramarginalis  encloses  the 
ascending  terminal  stem  of  the  ramus  posterior  of  the  Sylvian  fissure  and  is  bounded  by 
the  sulcus  intermedius  primus  behind.  The  gyrus  angularis  surrounds  the  ascending 
end  of  the  superior  temporal  fissure,  and  is  bounded  in  front  by  the  sulcus  intermedius 
primus  and  behind  by  the  sulcus  intermedius  secundus. 

Lobus  temporalis.  One  of  the  most  constant  fissures  is  the  sulcus  temporalis 
superior.  It  begins  in  front  at  the  temporal  pole,  extends  backward  and  upward  parallel 
to  the  fissura  cerebri  lateralis  and  ends,  as  a  rule,  in  the  gyrus  angularis  by  running 
upward  behind  the  ascending  terminal  branch  of  the  fissura  cerebri  lateralis.  At  times 
one  finds  a  forking  into  an  ascending  and  a  descending  branch.  The  sulcus  temporalis 
medius  runs  below  the  superior  temporal  fissure.  The  fissure  is  seldom  continuous, 
usually  being  made  up  of  several  parts.  Below  the  middle  temporal  fissure,  and  on  the 
basal  surface,  extends  the  sulcus  temporalis  iti/erior.  The  three  temporal  convolutions 
are  defined  by  these  fissures.  The  gyrus  temporalis  superior  extends  below  the  sulcus 
cerebri  lateralis  and  abo\e  the  superior  temporal  fissure  ;  the  gyrus  temporalis  medius 
lies  between  the  superior  and  middle  temporal  sulci ;  and  the  gyrus  temporalis  inferior 
is  located  below  the  inferior  temporal  fissure.  The  surface  of  the  upper  temporal  con- 
volution facing  the  Sylvian  fissure  presents  the 
gyri    temporales    transversi ,     also    known    as  "  '" 

the  convolutions  of   Heschl,  which  are  weakly      SkIc  a 
developed  in  the  front  half  and  more  strongly 
behmd.  /,„„/, 

Lcbus  occipitalis.     The  anterior  bound-  ^  , 

^  Sutc.  centrnlis  tn$uiae 

ary  of   the   lobus   occipitalis  is  formed   in  part  „„■     ,     c  a  <  .■        /  .v,    ■      i 

.'  ^  »  I'lG.  2  1. — Fissures  and  convolutions  of  the  insula. 

by  the  sulcus    occipitalis  transvcrsus,  a    sulcus 

liable  to  many  variations  respecting  its  position,  length  and  directicjn.  In  addition,  there  are 
the  sulci  occipitales  superiores  and  the  sulci  occipitales  laterales.  By  means  of  these  fissures 
the  gyri  occipitales  superiores  and  the  gyri  occipitales  laterales  are  defined.  Towards  the  oc- 
cipital pole,  the  convolutions  join  a  vertical  gyrus,  knf>wn  as  the  gyrus  desccndcns  (Ecker). 


22  MORPHOLOGY. 

Insula.  On  penetrating  the  depth  of  the  fissura  cerebri  lateraHs,  by  drawing 
apart  the  edges  of  the  bounding  lobes,  one  comes  to  a  deep  depression,  the  fossa 
cerebri  lateralis  {Sylvii),  at  the  bottom  of  which  lies  the  insula,  also  known  as  the  basic 
lobe  (Stammlappen).  Those  parts  of  the  lobes  bounding  the  Sylvian  fissure,  which  cover- 
in  the  island,  together  constitute  the  operculum.  Since  the  frontal,  parietal  and  temporal 
lobes  participate  in  its  production,  we  distinguish  a  pars  frontalis,  a  pars  parictalis  and 
a  pars  temporalis  of  the  operculum.  The  surface  of  the  temporal  lobe  directed  towards 
the  insula  presents  the  siclci  and  gyri  temporales  trayisversi.  Similar  fissures  and  con- 
volutions exist  also  upon  the  surfaces  of  the  parietal  and  frontal  opercula  facing  the 
island.  The  insula  appears  in  the  form  of  an  irregular  conical  projection,  a  three-sided 
pyramid  whose  apex — -the  islajid-pole — is  directed  forward   and  outward.       The    island   is 


Sulcus  paracentralls 


Sjtlc  parotfacior. 
post. 


lingua  Us 

Fissura  collateral. 
Sulcus  temporalis  inf. 


Fissura  rhinica     Fissura  hippocampi         Gyr.  fusiformis 
Fig.  22. — Medial  cerebral  surface.     Fissures  and  convolutions. 


encircled  by  a  deep  fissure,  the  sulcus  circularis  (Reili).  Since  this  furrow,  strictly 
considered,  is  not  circular  but  rather  triangular,  a  sulcus-  anterior,  a  sulcus  superior  and 
a  sulcus  hiferior  may  be  distinguished.  The  sulcus  anterior  separates  the  island  from 
the  orbital  part  of  the  frontal  operculum,  the  sulcus  superior  from  the  fronto-parietal 
operculum,  and  the  sulcus  inferior  from  the  temporal  operculum.  The  island  is  divided 
into  a  lobus  insulae  anterior  and  a  lobus  insulae  posterior  by  the  sulcus  centralis  insulae, 
a  fissure  that  runs  from  in  front  and  below  backward  and  upward.  The  anterior  lobule 
exhibits  several  short  convolutions,  the  gyri  breves  insulae,  while  the  posterior  lobule 
appears  as  the  gyrus  longus  insulae,  which  now  and  then  is  subdivided  into  two  con- 
volutions by  a  long  furrow  which  parallels  the  sulcus  centralis  insulae. 


LOBES    AND    GYRI   OF    THE    MEDIAL    AND    BASAL    SURFACES. 

All  four  cerebral  lobes,  with  which  we  have  now  become  somewhat  intimately 
acquainted  on  the  dorso-lateral  aspect  of  the  hemisphere,  are  continued  onto  the  medial 
and  partly  also  onto  the  basal  surface.  They  do  not  extend,  however,  over  the  entire 
medial  surface,  but  bound  a  large  annular  tract  that  belongs  to  the  rhinencephalon. 
Let  us  first  examine  the  defining  fissures  and  sulci. 


FISSURES   AND    CONVOLUTIONS. 


23 


The  sulcus  cinguli,  or  calloso-margmal  fissure,  begins  beneath  the  rostrum  of  the 
corpus  callosum.  It  runs  forward,  around  the  knee,  and  then  backward,  more  or  less 
parallel  with    the   corpus  callosum,  as  far   as    the    splenium.       Here    it    bends  at   a    blunt 


Gyrus 

higuli 

Sulcus  I 

■inpdi 

•Sulcus  par 
post. 

ol/act. 

Sulcus  par 
ant. 

olfact.. 

Br  oca' 

I  field 

Fig.  23. — Medial  ^ 


Ussurn 
•     '^y-  '"/"/"":■    campi  ralis 

ebral  surface.      Gyrus  fornicatus  i 


angle  upward  towards  the  superior  margin  of  the  hemisphere  as  the  ramus  margiyialis. 
During  its  entire  course,  several  and  sometimes  deep  incisions  branch  off,  upward  as 
well  as  downward.      In  front  of  the  obtuse    bend,   approximately  over    the   middle  of   the 


Sulcus  olfnctori 


Fig.  24. — Basal 


:  of  the  brain.      Fiss 


and  convolutions. 


corpus  callosum,  the  fissure  usually  sends  a  side  branch,  the  sulcus  paraceniralis,  upward. 
Another  branch,  the  sulcus  supraorbilalis  (Broca),  is  given  off  at  the  level  of  the  genu. 
Finally,  a  third  fissure,  the  sulcus  subparieialis,  which  represents  a  continuation  of  the 
chief  furrow,  runs  backward  and  around  the  splenium  corporis  callosi.  Immediately 
beneath  the  knee  and  the    rostrum    of    the  callosum,  the  sulcus  corporis  callosi   begins,  at 


24 


MORPHOLOGY. 


first  as  only  a  shallow  fissure.  It  often  appears  there  as  the  prolongation  of  the  sulcus 
parolfactorius  posterior  (see  Rhinencephalon,  page  26),  then  continues  around  the  genu, 
closely  follows  the  convex  surface  of  the  corpus  callosum,  runs  around  the  splenium 
and  continues  into  the  fissura  hippocavipi,  the  deep  cleft  that  runs  from  behind  and 
above  forward  and  downward. 

In  the  posterior  part  of  the  medial  surface  of  the  hemisphere,  beginning  about  mid- 
way between  the  turned-over  end  of  the  central  fissure  and  the  occipital  pole,  the  deep 
Jissura  parieto-occipitalis  runs  obliquely  forward  and  downward,  behind  the  lower  end 
of  the  subparietal  branch  of  the  sulcus  cinguli,  as  far  as  the  region  beneath  the  splenium 
corporis  callosi.  In  the  lower  part,  at  about  the  level  of  the  splenium,  the  furrow  is 
joined  at  an  acute  angle  by  the  deep  fissura  calcarina.  The  latter,  slightly  arched 
and  somewhat  above  the  medial  border,  extends  backward  toward  the  occipital  pole, 
where  it  may  end  as  a  simple  groove,  or,  as  is  usually  the  case,  in  two  widely  divergent 
branches.  Occasionally  the  calcarine  fissure  overruns  the  occipital  pole  and  terminates 
on  the  dorso-lateral  surface  of  the  hemisphere.  The  stem  formed  by  the  union  of  the 
parieto-occipital  and  calcarine  fissures  extends  downward  and  close  behind  the  hippo- 
campal  fissure,  without,  however,  joining  the  latter.  The  fissura  collateralis  begins  at 
the  level  of  the  occipital  pole,  below  the  calcarine  fissure,  and  passes  forward  below  the 
common  stem  of  the  parieto-occipital  and  calcarine  fissures.  Its  continuation  into  the 
anterior  part  of  the  temporal  lobe  constitutes  the  fisstii-a  rhinica,  whose  front  end  is 
known  as  the  incisura  temporalis  (Schwalbe).  Below  the  collateral  fissure  is  the  sulcus 
temporalis  inferior. 

By  means  of  the  foregoing  fissures,  the  following  parts  are  defined.  The  tract 
occupying  the  front  part  of  the  medial  surface  outside  the  sulcus  cinguli  belongs  to  the 
frontal  lobe,  more  particularly  to  the  superior  frontal  convolution.  It  extends  back- 
ward beyond  the  paracentral  sulcus,  its  posterior  limit  being  a  line  drawn  from  the 
medial  end  of  the  central  sulcus,  between  the  paracentral  and  marginal  rami  of  the 
sulcus  cinguli.  to  the  last-named  fissure.  The  tract  between  the  paracentral  and  mar- 
ginal branches  of  the  sulcus  cinguli  is  called  the  lobulus  paracentralis.  Here  is  found  the 
transition  of  the  gyrus  centralis  anterior  into  the  gyrus  centralis  posterior.  The  larger 
part  of  the  paracentral  lobule  belongs  to  the  precentral  convolution.  Behind  the  tract 
belonging  to  the  frontal  lobe,  a  region  broadens  'out  which  belongs  to  the  pai'ietal  lobe. 
It  Hes  above  the  sulcus  cinguli  and  its  prolongation,  the  subparietal  fissure,  and  is 
bounded  behind  by  the  parieto-occipital  fissure.  The  entire  tract,  between  the  marginal 
arm  of  the  sulcus  cinguH  in  front,  the  subparietal  fissure  below  and  the  parieto-occipital 
fissure  behind,  constitutes  the  praeameus  or  quadrate  lobule.  Between  the  parieto-occip- 
ital and  ■  calcarine  fissures  lies  the  cicneus,  which  belongs  to  the  occipital  lobe.  Below 
the  calcarine  fissure,  between  it  and  the  collateral  fissure,  lies  another  part  of  the  occip- 
ital lobe  known  as  the  gyrus  lingualis.  On  the  basal  aspect  of  the  hemisphere,  below 
the  collateral  fissure,  the  gyrus  fusiformis  extends  as  a  part  of  the  temporal  lobe.  It 
is  also  called  the  gyrus  occipito-teniporalis. 

A  large  annular  tract  belonging  to  the  rhinencephalon  is  enclosed  by  the  foregoing 
convolutions  and  lobes.  Externally  it  is  bounded  by  the  sulcus  cinguli,  the  common 
stem  of  the  parieto-occipital  and  calcarine  fissures,  the  front  end  of  the  collateral  fissure 
and  the  fissura  rhinica.      The  inner  boundary  is  contributed  by  the  sulcus    corporis  callosi 


RHlXHNCEi  HALON.  25 

and  the  fissura  hippocampi.  In  its  entirety,  this  tract  constitutes  the  gyrus  fornicatus 
or  the  limbic  lobe.  It  is  subdivided  into  the  gyrus  ctnguli,  which  arches  around  the 
corpus  catlosum,  and  the  gyrus  hippocampi,  which  is  included  between  the  hippocampal 
fissure  on  the  one  side  and  the  collateral  and  rhinal  fissures  on  the  other  and  hooks 
around  the  anterior  end  of  the  hippocampal  fissure  to  form  the  uncus.  The  gyrus 
cinguli  and  the  gyrus  hippocampi  are  continuous,  behind  and  beiow  the  splenium,  by 
means  of  the  isthmus  gyri fornicati. 

Turning  once  more  to  the  basal  surface,  in  the  posterior  and  larger  division,  we 
note  the  sulci  and  gyri  already  mentioned: — the  fissura  hippocampi,  the  fissura  parieto- 
occipitalis  and  calcarina,  joining  to  form  a  common  stem,  the  fissura  coUateralis,  the 
fissura  rhinica,  the  sulcus  temporalis  inferior  and  the  convolutions  extending  between 
these  furrows.  The  anterior  and  smaller  division  of  the  basal  aspect  belongs  to  the 
lobus  frontalis,  being  known  as  its  orbital  surface.  Near  the  medial  border  of  the  latter, 
the  straight  sulcus  olfactorius  runs  forwards  and  somewhat  medially  and  lodges  the 
olfactory  bulb  and  tract.  The  sulcus  is  deep  and  almost  always  extends  farther  forwards 
than  the  anterior  end  of  the  bulbus  olfactorius.  Behind,  it  divides  into  a  ramus  medialis 
and  lateralis,  which  embrace  the  tuberculum  olfactorium.  Lateral  to  the  olfactory  fissure 
lie  some  furrows  of  uncertain  number  and  arrangement,  the  sulci  orbitales.  By  their  union 
the  most  varying  patterns  are  produced,  including  H-,  X-,L-,T-,K-  and  Z  - 
like  forms.  ^Medial  from  the  sulcus  olfactorius  extends  the  gyrus  rectus.  The  gyn 
orbitales  are  bounded  b)'  the  orbital  fissures. 

RHINENCEPHALON. 

The  rhinencephalon  embraces  :  {a')  the  peripheral  division  and  (/')  the  central  or 
cortical  division. 

Thu  peripheral  division  includes  the  iobus  olfactorius,   to  whicli  belong : 
The  bulbus  olfactorius. 
The  tractus  olfactorius, 
The  tuberculum  olfactorium,  with  the  gyn 

olfactorii  medialis  and  lateralis, 
The  area  parolfactoria  {Broca), 
The  substantia  perforata  anterior, 
The  gyrus  diagonalis  rhinencephali. 
The  gyrus  subcallosus   {Zuckcrkandl). 

The  central  ur  cortical  division  includes: 

The  gyrus  fornicatus   {Arnold), 

The  hippocampus, 

The  gyrus  dentatus. 

The  gyrus  uncinatus. 

The  gyrus  intralimbicus. 

The  gyrus  fasciolaris. 

The  gyri   Andrt-ac   Retzii  or  callosal  gyn. 


26 


MORPHOLOGY. 


I.   LOBUS    OLFACTORIUS. 

The  olfactory  lobe  falls  under  two  subdivisions,  one  in  front,  the  lobiis  oLfadoriiis 
anterior,  and  one  behind,  the  lobus 
o/facforms  posterior  ( Figs.  25  and 
26).  These  are  separated  from 
each  other  by  a  fissure,  the  sul- 
cus parolfactorius  posterior  (the 
embryonic  Jissura  prima  of  His  J, 
which  runs  behind  the  trigonum 
olfactorium,  between  the  latter  and 
the  substantia  perforata  anterior, 
and  continues  toward  the  medial 
surface  of  the  hemisphere. 

To   the    lobus    olfactorius 
anterior  belong  : 

The    bulbus    olfactorius, 

The    tractus    olfactorius. 

The  tuberculum  olfac- 
torium and  the  di- 
verging gyri  olfactorii 
medialis  and  lateralis, 


The  area  parolfactoria. 


of  human  foetus  of  between  fiv 
Basal  aspect. 


Gyr 


oljact.   lateralis 


Sulc7is  parolfact.  Post. 


Gyrus  olfactorio-orbltalis 
Subst.  fierf. 


Anguhis  gyr    olf.  lateral. 


Gyr.  anthiens 
Sulc.  in/,  rhinencepk. 
Gyr.  sefnilunar 
Sulcus  sentiannularis 


Gyr.  olfactorins  tnedialis 
Br  oca's  diagon,  band 


p  raecontm  issurale 
(Lamina  terfninalis) 


Fig.  26. — Schematic  representation  of  the  lobus  olfactorius. 


LOBUS   OLFACTORIUS    ANTERIOR.  27 

To  the  lobus  olfactorius  posterior  belong : 

The  subtiantia  perforata  anterior  or  gyrus  perforatus  rhinencephali, 
The  diagonal  band  of  Broca,   or  gyrus  diagonalis  rhinencephali, 
The  gyrus  subcallosus. 

A.     LOBUS   OLFACTORIUS  ANTERIOR. 

The  bulbus  olfactorius  presents  usually  an  oval  form — an  ellipse  or  a  vertically 
flattened  band — and  constitutes  an  enlargement  of  the  tractus  olfactorius  in  front.  On 
the  under  surface,  delicate  threads,  the  fila  olfadoria,  pass  out  and  descend  into  the 
nasal  fossa  through  the  apertures  of  the  lamina  cribrosa.  They  are  disposed  in  two 
series  and  may  be  designated  as  the  fila  olfactoria  medialia  and  lateralia.  They  are  so 
delicate  that  they  are  always  broken  off  when  the  brain  is   remo\ed. 

The  tractus  olfactorius  lies  as  a  white  strand  in  the  olfactory  sulcus  and, 
on  cross-section,  reveals  the  form  of  a  triangle  with  base  below  and  ape.x  above  buried 
in  the  sulcus.  The  hind  part  of  the  tract,  toward  the  tuberculum  olfactorium,  is  narrow 
and  somewhat  compressed. 

The  tuberculum  olfactorium,  into  which  the  tractus  is  prolonged  behind, 
appears  in  its  true  form  only  after  the  bulb  and  tract  have  been  raised  from  the 
olfactory  sulcus  and  the  latter  itself  rendered  more  gaping  by  pulling  apart  the  bounding 
convolutions.  Then  the  tuberculum  appears  as  a  pyramidal  elevation,  whose  apex  pene- 
trates the  sulcus  and  whose  base  forms  an  irregular  triangular  held,  the  trigonum 
o/f actor ium. 

From  the  tuberculum  proceed  the  medial  and  lateral  olfactory  convolutions  whose 
courses  are  as  follows  : — 

The  gyrus  olfactorius  medialis  runs  as  a  narrow  convolution  medially.  In  front, 
it  is  bounded  by  the  medial  posterior  branch  of  the  sulcus  olfactorius;  medially  and 
behind,  by  the  sulcus  parolfactorius  posterior  (the  fissura  prima  of  His).  A  white  fascic- 
ulus of  fibres,  the  stria  olfactoria  medialis,  the  continuation  of  the  medial  strand  of  the 
olfactory  tract,  streams  into  the  gyrus  olfactorius  medialis,  soon  to  become  lost  in  the 
gray  substance  of  the  convolution. 

On  following  the  medial  gyrus  farther,  it  is  found  to  radiate  within  a  small  field 
on  the  medial  surface  of  the  hemisphere,  that  lies  immediately  below  the  rostrum  of  the 
corpus  callosum  and  is  bounded  both  in  front  and  behind  by  a  small  fissure.  The  furrow 
in  front  is  the  sulcus  parolfactoriics  anterior,  while  the  one  behind  is  the  continuation 
of  the  sulcus  parolfactorius  posterior,  already  mentioned.  The  small  field  is  called  the  area 
parolfactoria,  or  field  of  Broca.  It  joins  the  gyrus  olfactorius  medialis  with  the  gyrus 
fornicatus,  particularly  with  the  gyrus  cinguli  (Figs.  18  and  23),  and  thus  establishes  the 
connection  of  the  lobus  olfactorius  anterior  with  the  central  region  of  the  rhinencephalon. 

The  gyrus  olfactorius  lateralis  runs  laterally.  In  the  foetal  brain  of  from  four 
to  five  months,  one  readily  recognizes  that  the  gyrus  passes  outward  towards  the  Sylvian 
fos.sa,  its  so-called  front  limb  proceeding  from  the  trigonum  almost  at  right  angles ; 
then,  at  the  medial  margin  of  the  fo.ssa  and  after  an  acute  bend,  the  hind  limb  runs 
backward  and  medially  to  the  anterior  border  of  the  gyrus  hippocampi.  Here  the  gyrus 
ends,  to  a  certain  extent,  in  two  claws,  the  medial  one  of  which  is  known  as  the  gyrus 
semilunaris    rhinencephali,    and    the    lateral    as    the  gyrus    ambicns    rhinencephali.      The 


28 


MORPHOLOGY. 


fissure  separating  the  claws  is  the  su/cus  semiannularis  (Figs.  25  and  26).  In  conse- 
quence of  the  subsequent  strong  development  of  the  frontal  and  temporal  lobes,  which 
approach  each  other  more  and  more,  the  angle  formed  by  the  two  limbs  of  the  gyrus  olfac- 

torius  lateralis  becomes  progressively 
more  acute,  although  the  demarcation 
of  the  gyrus  from  the  insula  is  still 
distinct.  In  the  later  stages,  the  limbs 
become  more  closely  approximated  and 
the  apical  part  of  the  convolution  is 
incised  by  the  sulcus  centralis  iiisiclae, 
which  meanwhile  has  been  formed.  The 
result  is,  that  the  previous  connection 
of  the  two  limbs,  as  well  as  the  de- 
marcation of  the  con\-olution  towards 
the  insula,  vanishes,  the  convolution 
now  appearing  to  expand  within  the 
substance  of  the  insula. 

Since  these  relations  persist    in  the 

adult,   it    was    assumed    that    the    lateral 

olfactory     convolution,     which    bounds    the    insula    medially,    belonged    to    the    island  ; 

hence     it    was    designated  the    linien    insiilae.       The    latter,    however,    belongs    to    the 

rhinencephalon  and  represents   the  gyrus   olfactorius  lateralis,   which  is  subdivided  into  a 


-  Schematic  representation   of   the   gyrus   olfactorius 
lateralis  in  the  foetal  brain. 


Fig.   28. — Oblique  mesial  aspect  of  the  br: 


'bmaris 
human  foetus  of  four  months.     Photograph. 


front  and  hind  limb — pars  anterior  and  posterior.      The  area    enclosed  by   the  limbs    was 
named  by  Retzius,   the  angiihis  gyri  olfactorii  lateralis. 

The   pars    anterior   usually    appears   as    a   fairly    broad    convolution,    which    extends 
from   the  tuberculum   olfactorium   outward  and  somewhat  obliquely  backward  and  is  sep- 


LOBUS   OLFACTORIUS    POSTERIOR. 


29 


arated  from  the  substantia  perforata  anterior  by  a  fissure,  the  sulcus  arcuatus  rhinen- 
cepfiali,  that  follows  the  gyrus  olfactorius  lateralis  medially  as  far  as  the  gyrus  hippocampi. 

Laterally  and  in  front,  the  pars  anterior  joms  the  orbital  convolution  to  form  the 
gyrtis  olfadorio-orbitalis  of  Retzius,  which  medially  is  bounded  by  the  postero-lateral 
branch  of  the  sulcus  olfactorius.  The  gyrus  is  commonly  simple,  but  may  be  divided 
into  IWO  parts  by  a  short  fissure ;  likewise,  it  may  be  subdi\ided  by  a  longitudinal 
fissure  into  two  subsidiary  convolutions,   an  anterior  and  a  posterior. 

The  stria  olfadoria  lateralis  passes  as  a  white  fibre-bundle  outward  along  the  pars 
anterior  toward  the  angulus  gyri  olfactorii  lateralis,  here  lying  quite  near  the  substantia 
perforata  anterior.  It  then  bends  backward  in  the  angle  and  later  disappears.  Occa- 
sionally the  lateral  olfactory  root  consists  of  two  bundles,  of  which  the  medial  follows 
the  border  of  the  substantia  perforata,  until  it  is  finally  lost  within  the  substance.  It  is 
to  be  further  noted,  that  a  third  or  middle  root  may  be  found  between  the  lateral  and 
medial  ones.      It  soon  vanishes,   however,   within  the  substantia  perforata. 


Anterior 
end  of  temporal  lo6e 

Fig.  29. — Region  around  the  tip  of  the  temporal  lobe  of  the  adult  brain.     Photograph. 

After  recurving  in  the  anj^le,  the  lateral  olfactory  convolution,  as  the  hind  limb 
or  pars  posterior,  continues  inward  and  backward  toward  the  front  end  of  the  gyrus 
hippocampi. 

On  e.xamining  more  closely  the  antero-median   surface   of  the  gyrus  hippocampi  in 

the  adult    brain,    one    sees    the  convolutions   in   which    the    posterior    limb  fades    away — 

the  gyrus  semilunaris  medially  and  the  gyrus  ambiens  laterally.  The  gyrus  ambiens 
arches  around  the  gyrus  semilunaris  and  then  is  lost  within  the  uncus. 


M.     LOBUS  OLFACTORIUS  POSTERIOR. 

The  substantia  perforata  anterior  is  an  oblique  quadrangular  field  lying  behind 
the  trigonum  olfactorium,  between  the  latter  and  the  tractus  opticus.  It  exhibits  numer- 
ous small  openings  for  the  passage  of  blood  vessels,  especially  in  its  anterior  part  in  the 
vicinity  of  the  trigonum.  This  front  part  constitutes  the  substantia  perforata  anterior 
proper,    the  gyrus  perforatus  rhincncephali. 


30  MORPHOLOGY. 

The  posterior  part,  bordering-  the  tmctus  opticus,  differs  from  the  anterior  chiefly 
in  its  Hghter  color  and  smoother  surface.  This  part  is  known  as  the  dtt7oo//ii/  band  of 
Broca,   or  the  ^rnts  diao-o/ia/r's  rhinenccplnxli. 

Gyrus  perforatus  and  gyrus  diag-onalis  form  the  essential  features  of  the  lobus 
olfactorius  posterior.  To  the  latter  belongs  an  additional  small  field  on  the  medial  sur- 
face of  the  hemisphere,  the  gyru^  siibcalhysus  of  Zuckerkandl.  This  field  is  easily 
located,  since  it  is  continuous  with  the  diagonal  band  of  Broca,  lying  behind  the  area 
parolfactoria,  separated  from  tlie  latter  by  the  sulcus  parolfactorius  posterior,  and  ia 
front  of  the  commissura  anterior  and  the  lamina  rostralis  (Fig.    iS). 

The  gyri  subcallosi   ^the  stalks  of  the    callosum  of  Broca)   descend  close  together 

from  the  rostrum  of  the  corpus 
callosum.  They  are  separated  from 
each  otlier  by  a  medial  furrow, 
the  sulcus  subcallosus  medianus  of 
Retzius,    and  form    the   narrow   tri- 

^'"ff'^siocV"^       gonum  praccomniissurak,  which  lies 

in  front  of  the  anterior  commissure 
and  belong-s  to  the  lamina  praccom- 
missuralis.  The  latter  is  a  thin 
lamella  that  co\ers  the  anterior  com- 
missure  and    passes    over    into    the 

Pig.  30. — Middle  region  of  the  brain-base  of  a  human  foetus.  3.1.5        lamina     terminalis.  At     the     lower 

«u.  long.  At  each  side  of  the  chiasma  is  seen  the  substantia  per- 
forata anterior,  with  the  diagonal  band  of  Broca.  (His.)  border  of  the  precommissural  tri- 
gone, the  two  gyri  subcallosi  di\-erge 
at  almost  right  angles  and  proceed,  on  each  side,  outward  and  backward  along  the 
optic  tract  as  a  ^^•hite  band,  the  diagonal  band  of  Broca,  to  reach  the  front  end  of  the 
gyrus  hippocampi. 

Broca's  band  is  disting-uished  by  its  lighter  color  from  the  deeper  tinted  sub- 
stantia perforata  anterior  ;  further,  the  disposition  and  form  of  the  \-ascular  foramina  are 
cliaracteristic.  These  are  oval  or  elliptical,  their  longer  diameters  paralleling  the  a.xis 
of  Broca's  band.  Although  the  band  is  always  present,  it  is  not  always  plainly  \-isible, 
in  some  cases  it  being-  superficial  only  in  certain  places,  while  in  others  it  is  buried 
beneath  a  laver  of  gray  substance  that  must  be  removed  before  the  band  is  seen. 


J.     GYRUS    FORXICATUS. 

To  the  peripheral  region  of  the  rhinencephalon,  the  lobus  olfactorius,  is  attached 
tlie  central  district.  Here  the  gyrus  fornicatus  first  claims  closer  attention.  It  is  an 
annular  tract  on  the  medial  surface  of  the  hemisphere,  encircled  by  the  cerebral  mantle 
and  composed  of  two  chief  convolutions,  the  gyrus  cinguli  and  the  gyrus  hippocampi, 
connected  with  each  other  by  means  of  the  isthmus. 

The  gyrus  cinguli  forms  the  arching  convolution,  paralleling  the  convex  upper 
surface  of  the  corpus  callosum,  between  the  sulcus  cinguli  and  the  sulcus  corporis 
callosi.  It  presents  numerous  \-ariations  in  consequence  of  the  inconstant  relations  of 
tlie  sulcus  cinguli.      The  latter,   in  fact,   does    not  represent  a  simple  fissure,   but  consists 


GYRUS    FORNICATUS.  31 

of  several  parts,  known  as  the  pars  anterior,  pars  intermedia  and  pars  posterior.  As  a 
result,  numerous  annectant  or  bridging  convolutions  arise,  which  unite  the  gyrus  cinguli 
with  the  neighboring  convolutions  of  the  pallium.  When  the  composite  parts  join  to 
form  a  simple  sulcus,  the  course  already  described  (page  22)  as  typical  is  observed. 
In  its  entire  path,  several  incisions,  some  deep,  branch  toward  the  frontal  lobe,  while 
those  passing  into  the  gyrus  cinguli  are  few  and  mostly  short.  The  surface  of  the  gyruS 
cingiili  e.xhibits  likewise  some  shallow  furrows.  Owing  to  these  peculiarities,  as  well 
as  to  its  smooth  surface,  the  gyrus  is  more  or  less  clearly  defined  from  the  adjacent 
convolutions.  Accordingly,  the  gyrus  cinguli  takes  the  following  course.  It  begins 
narrow  beneath  the  knee  of  the  corpus  callosum,  as  the  direct  continuation  of  Broca's 
field.  In  its  further  course,  around  the  genu  and  over  the  truncus  corporis  callosi,  the 
convolution  is  broader.  Farther  behind,  at  the  bend  around  the  splenium,  it  again 
distinctly  narrows  and,  where  it  is  deeply  incised  by  the  fissura  parieto-occipitalis,  passes 
over  into  the  isthmus  gyri  fornicati. 

When  the  sulcus  cinguli  does  not  form  a  simple  furrow,  the  convolution  assumes 
an  entirely  different  character.  Doubling  and  splitting  of  the  convolution  may  exist,  as 
well  as  separation  into  two,  three  or  four  parts.      Ccuicerning  the  annectant  convolutions. 


fh!u 


F!s.nr.  rkinua     Cyr.  kippoc.    ^j^f/T         '^f^f 
Fig.  31. — Medial  cerebral  surface.     Gyms  fomicatus  is  shaded. 

it  may  be  noted  that  of  these  one  is  fairly  constant  in  the  fore  part  of  the  g>'rus 
cinguli  and  establishes  a  connection  between  the  latter  and  the  gyrus  frontalis  superior. 
A  second  annectant  convolution  is  found  in  the  middle  portion,  the  connection  between 
the  gyrus  and  the  lobulus  paracentralis,  while  a  third  appears  in  the  posterior 
division,  providing  continuity  with  the  praecuneus.  The  last  connection  is  often 
double  in  consequence  of  the  sulcus  subparietalis  existing  as  a  separate  furrow  and 
not  as  the  hind  part  of  the  chief  fissure.  In  such  cases  the  gyrus  cinguli  appears  to 
radiate  into  the  praecuneus. 

The  chief  variations  of  the  gyrus  cinguli  are  found  mosdy  in  its  front  part. 
Here  the  convolution  may  be  doubled  by  an  inner  or  outer  parallel  fissure. 
If  an  outer  secondary  fissure  be  present,  the  gyrus  cinguli  proper  appears  markedly 
narrowed  at  the  knee  of  the  callosum  ;  in  such  case,  the  convolution  lying  between  the 
sewndary  fissure  and  the  sulcus  cinguli  proper  must  be  reckoned  as  part  of  the  gyrus 
cinguli. 


32  MORPHOLOGY. 

The  delimitation  of  the  gyrus  becomes  more  difficult  when  it  consists  of  several 
pieces.  Then  each  portion  behind  appears  as  a  wedge  beneath  the  part  in  front,  and 
the  entire  convolution  is  markedly  narrowed,  particularly  towards  the  genu  corporis  callosi. 
The  convolution  appears  notched  in  its  upper  part.  For  this  reason  Rolando  compared 
it  to  a  cock's  comb  and  called  it  the  ''ridged  convolution";  hence  also  the  designation 
of  the  sulcus  cinguli  as  the   "festooned  fissure"    (Pozzi). 

In  consequence  of  the  deep  incision  into  the  gyrus  fornicatus  by  the  common  limb 
of  the  parieto-occipital  and  calcarine  fissures  behind  the  splenium,  the  isthmus  is  pro- 
duced ;  this  marks  the  transition  of  the  gyrus  cinguli  into  the  gyrus  hippocampi. 

The  gyrus  hippocampi  proceeds  forward,  becomes  broader  and,  at  the  level  of 
the  substantia  perforata  anterior,  bends  around  the  front  end  of  the  fissura  hippocampi 
to  form  the  uncus.  On  its  outer  side,  the  gyrus  hippocampi  is  bounded  by  the 
common  stem  of  the  parieto-occipital  and  calcarine  fissures,  the  anterior  part  of  the 
collateral  fissure  and  the  fissura  rhinica. 

As  the  gyrus  cinguli,  so  also  the  gyrus  hippocampi  exhibits  connections  with  the 
convolutions  lying  to  its  outer  side.  In  this  relation  the  great  variability  of  the  fissura 
collateralis  comes  into  consideration.  When  the  fissura  rhinica  is  connected  with  the 
fissura  collateralis,  two  annectant  convolutions  are  found,  an  anterior  and  a  posterior. 
The  former,  the  gyrus  rhinencephalo-temporalis  anterior,  joins  the  front  part  of  the 
gyrus  hippocampi  with  the  temporal  pole  and  is  one  of  the  most  constant  bridges.  The 
other,  the  gyms  rhinencephalo-Hngualis,  connects  the  gyrus  hippocampi  with  the  gyrus 
lingualis.  The  last-named  bridge  is  mostly  superficial,  but  may  present  mani- 
fold variations.  It  may  be  divided  by  a  longitudinal  furrow  into  two  parts,  of  which 
one  or  the  other  is  deeply  placed  and  the  remaining  one  is  superficial.  Quite  rarely, 
the  entire  bridge  may  be  deeply  situated,  in  which  case  the  collateral  fissure  ends  in  the 
calcarine.  In  the  event  of  the  fissura  rhinica  being  separated  from  the  fissura  collater- 
alis,  a  third  bridge,   the  gyms  7-hinencephalo-fiisiformis,   is  present. 

The  surface  of  the  gyrus  hippocampi,  from  where  the  gyrus  approaches  the 
hind  end  of  the  callosum  forward,  particularly  toward  the  bottom  of  the  fissura 
hippocampi,  exhibits  a  lighter  color.  This  tract  is  known  as  the  substantia 
reticu/aris  alba  (Arnold).  Moreover,  mention  must  be  made  of  the  peculiar  character 
of  the  surface  of  that  part  of  the  gyrus  which  lies  between  the  fissura  rhinica  and 
the  fissura  hippocampi.  Here  the  surface  is  covered  with  numerous  small  nodules 
or    wartlike    ele\-ations,    designated   as  vermcae  gyri  hippocampi. 

3.     HIPPOCAMPUS. 

The  hippocampus  or  cornu  Ammonis  also  belongs  to  the  central  region  of  the 
rhinencephalon.  Since  this  structure  is  seen  only  after  the  lateral  ventricle  has  been 
opened,   its  further  consideration  will  be  postponed   (page  43). 

4.     GYRUS   DENTATUS. 

When,  in  order  to  determine  the  depth  of  the  hippocampal  fissure,  the  gyrus 
hippocampi  is  pulled  downward,  one  sees  a  gray  notched  or  corrugated  band,  the 
fascia  dentata   ( Tarini)   or  the  gyms  dentatus  of   Huxley.      Farther  inward  and  over  the 


GYRUS    DENTATUS. 


33 


gjTus  dentatus,  is  seen  a  white  band,  which  passes  from  the  uncus  gyri  hippocampi 
backward ;  this  is  the  fimbria  hippocanipi.  In  its  further  course  the  fimbria  is  con- 
tinuous with  the  fornix. 


Corpu 

s  Ciillosum 

Sept,; 

ft  pelluc'ui. 

Gyms  snbcallosits 
{Zuckerkandl) 

Corpus 

mnmllUre 

ClacoK 

tini's  hand 

Gyrus 

intralimb. 

.  hlfM 


Induseunt  ^iseum 


Fornix  trnni.vers. 
Fasciola 


Gyrus  /asciolaris 
Fiss.  hippocampi 

Gyrus  d^ittntus 
Sulcus  Jimbriodentnttis 


Fig.  32. — Relations  of  the  dentate  gyrus.     Gyrus  dentatus  is  red;  fimbria  and  forni-\  are  yellow. 

The  gyrus  dentatus  is  separated  from  the  gyrus  hippocampi  by  the  fissura  hippo- 
campi, and  from  the  fimbria  by  the  sulcus  fimbrio-dentatus.  Following  the  dentate 
gyrus  farther  backward,  it  is  seen  to  run  at  first  parallel  with  the  fimbria  to  the 
splenium  corporis  callosi.  Here  the  gyrus  leaves  the  fimbria,  loses  its  incisions  and 
knobs,  becomes  smooth  and,  as  the  fasciola  cinerea,  passes  around  the  callosum  to 
spread  out  over  the  latter  as  a  thin  lamella  of  gray  substance,  the  induseum  griscum. 
In  the  middle,  the  induseum  exhibits  the  striae  longitudinales  mediales  or  striae  Lancisii, 
while  on  each  side,   in  the  sulcus  corporis  callosi,  lies  the  stria  longitudinalis  lateralis  or 


Fig.  :i3. — Induseum  and  striae  lonKitudinales  on  the  uppe 


terhemisph 


of  the  corpus  callc 


taenia  tecta  (Fig.  33,).  Induseum  and  striae  longitudinales  run  forward  around  the 
knee  of  the  callosum  and  in  their  farther  course  pass  into  the  gyrus  subcalhjsus,  with 
ivhich,   in  turn,   Broca's  band  (page  30J  joins. 

According  to  most  authors,  the  fasciola  cinerea  constitutes  the  direct  continuation 
of  the  gyrus  dentatus.  As  shown  by  Retzius,  however,  the  gyrus  dentatus  is  not  pro- 
longed directly  into  the  fasciola  cinerea  (Fig.  34).  On  examining  the  area  beneath  the 
splenium  where  the  gyrus  dentatus  leaves  the  fimbria,  a  thin  strand  is  seen  next  the 
fascia  dentata,  which  likewise  sinks  into  the  depth  of  the  sulcus  fimbrio-dentatus 
?, 


34  MORPHOLOGY. 

between  the  fascia  dentata  and  the  fimbria.  This  small  cylindrical  strand  was  called  by 
Retzius  the  gyrtis  fasciolaris.  It  is  separated  from  the  gyrus  dentatus  by  a  small 
furrow,  the  sulacs  dejitato-fasciolaris,  and  forms,  by  union  with  the  pointed  end  of  the 
gyrus  dentatus,  the  fasciola  cinerea  of  the  authors.  The  fasciola  extends  as  a  gray  semi- 
cylinder  strand  around  the  splenium  and,  on  the  surface  of  the  callosum,  continues  as 
a  broad  plate,   the  gyrus  cpicallosus  (Retzius)  or  induseiim  griseion. 


Gyrus  /, 


Fascia  detitata 
Gyri  Andrene  Retzii 


Fig.  34. — Gyrus  fasciolaris  and  gyri  Andreae  Retzii. 

Retzius  agrees  with  Zuckerkandl,  that  the  striae  longitudinales  mediales  and 
laterales  correspond  to  local  elevations  of  the  induseum.  In  front,  they  pass  into  the 
gyrus  subcallosus  and  also  in  part,  at  least  so  far  as  the  taenia  tecta  is  concerned,  into 
the  substance  lying  lateral  to  this  gyrus.  Retzius  further  notes,  that  a  portion  of  the 
gray  lamella  covering  the  callosum  branches  off  at  the  posterior  limit  of  the  splenium  to 
continue  on  the  lower  surface  of  the  latter  and  there  form  an  induseran  inferius.  Since 
this  structure  often  resembles  a  convolution,  it  has  been  designated  by  Retzius  as  the 
gyrus  subsplenialis. 

Following  the  gyrus  dentatus  forward,  the  gyrus  hippocampi  being  drawn  down- 
ward, one  perceives  that  the  dentate  gyrus  here ,  likewise  gradually  separates  from  the 
fimbria  and  then,  after  a  bend  at  right  angles — the  angulus  gyri — passes  as  a  smooth 
slightly  convex  band  onto  the  uncus.  This  band  of  Giacomt7ii,  as  it  is  termed,  passes 
over  the  under  surface  of  the  uncus,  from  the  outer  side  onward  and  somewhat  back- 
ward, and  thence  continues  onto  its  upper  surface.  The  band  courses  from  the  inner 
side  forward  and  outward,  as  far  as  a  thin  sheet  of  medullary  substance,  the  velum 
terminale  (Abbey),  adhering  to  the  uncus.  This  entire  course  is  plainly  exposed  after 
removal  of  the  gyrus  hippocampi. 

Retzius  recognizes  two  divisions  of  the  gyrus  dentatus,  a  longitudinal  and  a 
transverse.  The  former,  proceeding  from  the  angulus  gyri  dentati,  extends  backward 
within  the  fissura  hippocampi.  The  transverse  division,  on  the  contrary,  proceeding 
from   the  angulus,   represents   the  front   end  of  the   convolution.       The   transverse   part — 


GYRUS    UNCINATUS.  35 

the  limbiis  Giacomini — is  further  subdivided  into  a  pars  occulta,  which  lies  buried  in  the 
hippocampal  fissure,  and  a  pars  aperta,  which  is  visible  on  the  upper  surface  of  the 
uncus.  In  front,  the  pars  occulta  is  limited  by  a  furrow  that  corresponds  morphologi- 
cally to  the  end  of  the  fissura  hippocampi.  Behind,  the  limitation  is  usually  less  definite, 
at  times  the  limbus  Giacomini  appearing  to  pass  over  into  this  part. 


Ciacomiurs  band 


Fig.  35. — Giacomini's  band.     The  under  surface  of  the  uncus  is  exposed  by  removing  part  of  the  gyrus  hippocampi. 

On  the  portion  of  the  under  surface  of  the  uncus  lying  in  front  of  Giacomini's 
band,  one  distinguishes  two,  often  only  one,  or  occasionally  three,  sulci  and 
included  convolutions,  which  pass  from  the  anterior  limiting  fissure.  These  are 
designated  as  the  sidci  and  gyri  digitati  extemi.  Small  tip-like  extensions  of  the 
Giacomini  band  radiate  forward  for  a  short  distance  within  the  sulci  digitati ;  conse- 
quently, this  part  of  the  limbus  appears  more  or  less  festooned.  The  anterior  termi- 
nation of  Giacomini's  band  is  as  yet  undetermined. 


5.    GYRUS   UNCINATUS,  GYRUS   INTRALIMBICUS  AND   GYRUS 
FASCIOLARIS. 

According  to  most  authors,  the  uncus  gyri  hippocampi  or  the  gyrus  uncinatus,  is 
the  continuation  of  the  gyrus  hippocampi,  bent  around  the  anterior  end  of  the  hippo- 
campal fissure,  which  extends  as  far  as  the  beginning  of  the  fimbria  and  is  divided  into 
an  anterior  and  posterior  part  by  the  Giacomini  band.  According  to  Retzius,  however, 
the  front  division  of  the  uncus  must  differ  morphologically  from  the  posterior.  He 
regards,  therefore,  the  anterior  part  as  belonging  to  the  gyrus  hippocampi  and 
designates  this  part  alone  as  the  gyms  uncinatus;  the  region  lying  behind  the 
Giacomini  band  constitutes  the  gyrus  intralimbicus  of  Retzius.  This  intralimbic 
gyrus  appears  sometimes  as '  a  small  slightly  arched  surface,  sometimes  as  one  or 
several  knobs,  and  occasionally  is  sharply  defined  by  a  fissure  from  the  fimbria  and 
the  gyrus  dentatus.  The  convolution  continues  for  a  short  distance  backward  within 
the   sulcus  Jimbrio-dcntatus.      Farther    behind    in    the    same    sulcus,    a  gray    strand  again 


36 


MORPHOLOGY. 


appears.  This  gradually  thickens,  lies  attached  to  the  gyrus  dentatus,  or  separated 
from  the  latter  by  the  sulcus  dentato-fasciolaris,  and,  as  the  gyrus  fasciolaris  of 
Retzius,   passes  around  the  splenium  corporis  callosi. 


6.    GYRI    ANDREAE    RETZII. 

These,  also  known  as  the  callosal  convolutions,  represent  rudimentary  gyri,  which 
appear  as  round  or  oval  elevations  on  the  medial  surface  of  the  gyrus  hippocampi, 
beneath  the  splenium  and  in  the  angle  formed  by  the  dentate  and  hippocampal  gyri. 
They     are    not    constant    and    may    be    little    more     than    mere    suggestions,    or,    when 

strongly  developed,  maj- 
resemble  a  spirally  wound 
cord.  Zuckerkandl-  desig- 
nates them  as  callosal 
convohdions ,  and  Giacomini 
reckons  them,  in  view  of 
their  structure,  as  belong- 
ing to  the  hippocampus. 
G.  Retzius  named  the 
convolutions  in  honor  of 
their  discoverer,  Anders 
Retzius,  his  father,  the  gyri 
Andrcae  Retzii  (Fig.  34). 
Summary.  ■  Taking 
a  general  survey  of  the 
entire  rhinencephalon  (Fig. 
36),  we  distinguish  a  periph- 
eral and  a  central  region. 
The  peripheral  region  includes  a  front  and  a  hind  part,  the  lobus  olfactorius 
anterior  and  the  lobus  olfactorius  posterior.  The  central  region  embraces  a  large 
annular  tract  on  the  medial  surface  of  the  hemisphere,  and  includes  the  gyrus  fornicatus 
and  the  gyrus  dentatus. 

Peripheral  and  central  regions  are  closel)'  united  with  each  other,  the  lobus 
olfactorius  anterior  being  connected  with  the  gyrus  fornicatus  and  the  lobus 
olfactorius  posterior  with  the  gyrus  dentatus.  Moreover,  the  lobus  olfactorius  anterior  is 
connected,  on  the  one  hand,  with  the  gyrus  cinguli  by  means  of  the  gyrus  olfactorius 
medialis  and,  further  along,  the  area  parolfactoria  ;  on  the  other  hand,  it  is  joined 
with  the  front  end  of  the  gyrus  hippocarnpi  by  means  of  the  gyrus  olfactorius 
lateralis.  The  lobus  olfactorius  posterior  is  connected  with  the  gyrus  dentatus  by 
means  of  Broca's  diagonal  band,  the  gyrus  subcallosus  and  the  induseum  covering 
the  corpus  callosum.  As  will  appear  later,  the  olfactory  centre  is  supposed  to  lie 
chiefly  in  the  cortex  of  the  gyrus  hippocampi.  Therefore,  the  impulses  transmitted 
from  the  nasal  mucous  membrane  by  the  fila  olfactoria  must  be  carried  from  the 
bulbus  olfactorius  and  transferred  to  the  central  region  of  the  rhinencephalon.  The 
course  of  this  olfactory  tract  will  best  explain  the  connections  of  the  individual  parts 
of  the  rhinencephalon   (page   144). 


Fig.  36. — Schematic  representation  of  the  regions  of  the  rhinencephalon: 
Yellow — lobus  olfactorius  anterior  and  gyrus  fornicatus;  red — lobus  olfactorius 
posterior  and  gyrus  dentatus. 


LAMINA   TERMINALIS. 


37 


PARS   OPTICA   HYPOTHALAMI. 

This  division  of  the  telencephalon  includes  : 
The  lamina  terminalis, 

The  chiasma  opticum,   with  the  tractus  optici, 
The  tuber  cinereum, 
The  infundibulum, 
The  hypophysis. 

fornix  Foramen  Monroi 


^Ittssa   intermedia 


Gyr 


■hlgllli 


snhcallosns  ~  -- 


Area  paroifacinri 
(Broca-s  fieUi 


ugh  the  lower  part  of  the  brain 


The  lamina  terminalis,  or  end-plate,  rises  as  a  thin  sheet  in  front  of  the  chiasma 
opticum  and  continues  in  front  of  the  commissura  anterior  and  the  columnae  fornicis. 
Between  it  and  the  chiasma  lies  the  ircessus  opticus.  The  thin  lamella  originally  formed 
the  middle  part  of  the  front  wall  of  the  fore-brain  ;  later  it  is  displaced,  lies  more  deeply, 
and  then  forms  the  anterior  wall  of  the  third  ventricle,  in  whose  roof-plate  it  is  continued. 

The  chiasma  opticum  forms  a  white  quadrangular  plate,  from  the  anterior  cor- 
ners of  which  proceed  the  7icrvi  optici  and  from  the  posterior  corners  the  tractus  optici. 
The  latter  run  as  flattened  cords  outward  and  backward  along  the  hind  border  of  the 
substantia  perforata  anterior ;  after  passing  around  the  pedunculi  cerebri  and,  farther 
along,  above  and  somewhat  lateral  to  the  vincus  gyri  hippocampi,  they  lead  into  the 
region  of  the  metathalamus. 

The  tuber  cinereum  lies  behind  the  chiasma,  bounded  laterally  by  the  optic 
tracts  and  the  cerebral  jieduncles  and  behind  by  the  corpora  mamillaria.  This  gray 
elevation  is  a  thin  lamina  and  assists  in  forming  the  floor  of  the  third  ventricle.      Traced 


38 


MORPHOLOGY. 


forward,  it  passes  into  the  lamina  terminalis,  and  in  this  anterior  position  is  pushed  into 
the  ventricle  by  the  chiasma.  Below,  the  tuber  cinereum  is  continuous  with  a  hollow 
funnel-shaped  structure,  the  infundibulum,  whose  cavity  is  known  as  the  recessus  771/201- 
dibuli.  To  the  end  of  the  infundibulum  is  attached  the  hypophysis  cereb)'i  or  pituitaty 
body,  a  gray  mushroom-shaped  structure,  about  the  size  of  a  bean,  whose  longest  diam- 
eter is  placed  transversely. 

The  hypophysis,  on  being  sectioned,  is  seen  to  be  composed  of  a  larger  anterior 
and  a  smaller  posterior  lobe.  Genetically,  only  the  posterior  lobe  belongs  to  the  brain, 
as  a  ventral  evagination  from  the  diencephalon.  The  lobus  anterior  originates  as  an 
evagination  from  the  embryonal  oral  recess.  In  consequence  of  constriction  and  isolation, 
the  evagination  later  gives  rise  to  the  hypophysial  \'esicle,  which  subsequently  trans- 
forms into  the  gland-like  structure  that,  as  the  anterior  lobe,  becomes  united  with  the 
lobus  posterior. 

Further,  at  particular  points  of  the  tuber  cinereum,  one  often  notes  small  evagina- 
tions.  One,  located  mostly  medial  and  immediately  in  front  of  the  corpora  mamillaria, 
has  been  named  by  Retzius  the  eminentia  saccularis,  while  the  smaller  and  lateral  eleva- 
tions are  the  eminentiae  laterales.  In  Fig.  30  the  eminentia  saccularis  is  plainly  seen. 
It  represents,  perhaps,  a  rudiment  of  the  saccus  vasculosus  strongly  developed  in  the 
bony  and  cartilaginous  fishes. 


INTERNAL  CONFIGURATION   OF  THE  TELENCEPHALON. 

The    examination    of   the    inner    configuration   of   the   end-brain   is   carried  out  most 
advantageously  in  the  following  manner.     A  brain  is  laid  on  its  base  and  the  removal  of 

the  hemispheres  is  begun.  This  is  ac- 
complished by  passing  horizontally,  with 
slow  continuous  stroke,  a  long  brain- 
knife  from  the  convex  lateral  surface  of 
the  hemisphere  as  far  as  the  longitudinal 
cerebral  fissure.  In  this  manner  first 
the  right  and  then  the  left  hemisphere 
are  removed,  from  above  downward,  in 
disk-like  pieces  about  one  centimeter 
thick.  The  last  horizontal  section  should 
fall  about  5  mm.  above  the  dorsal  surface 
of  the  corpus  callosum. 

Each  section  distinctly  exhibits  two 
different  substances — the  white  substance, 
light  in  color  and  situated  in  the  interior, 
and  the  gray  substance,  which  every- 
where encloses  the  former  and  continues 
as  a  band  at  the  periphery  (Fig.  38). 
In  the  first  pieces,  the  white  substance 
is  less  voluminous  than  the  gray.  The  deeper  one  cuts,  however,  the  greater 
the    amount    of     white    substance    revealed,    and    in    the     last     section,     passing    imme- 


FlG.   38. — Horizontal    section    through    the    cerebral    hi 
spheres,  showing  white  and  gray  substance. 


CEREBRAL   CORTEX. 


39 


diately  above  the  callosum  (Fig.  39),  in  each  hemisphere  is  seen  a  large  white  medul- 
lary field,  the  cenfnun  setniovale  fVieussens),  which  peripherally  is  bounded  by  the  gray 
band  representing  the  cerebral  cortex,   the  substantia  corticalis. 


striae  longititd.  medial. 


Radiatio  corpor.  callo^i 
{Fars  frontalis) 


Radiatio  corpor.  callosi 

{Pars  temporal,  and 

occipitalis) 


Fig.  39.— Horizontal  section  at   the  level  of  the  corpus  callosum.  showing  radiation  of  callosal  fibres. 


The  substantia  corticalis  is  not  everywhere  equally  developed  as  to  thickness,  in 
this  respect  varying  according  to  the  region  of  the  brain.  In  general,  the  cerebral 
corte.x  is  more  developed  on  the  summit  of  the  convolutions  and  less  so  at  the  bottom 
of  the  fissures,  being  thicker  on  the  outer  conve.x  surfaces  than  on  the  medial  and  basal 
a.spects  of  the  hemispheres.  The  corte.x  reaches  its  maximum 
development  in  the  upper  part  of  the  central  convolutions  and  in 
the  lobus  paracentralis,  and  its  minimum  in  the  occipital  pole. 
When  closely  examined,  even  with  the  unaided  eye,  one  recognizes 
that  the  cerebral  cortex  is  not  homogeneous,  but  is  composed  of 
alternating  gray  and  white  strata  arranged  parallel  with  the  surface. 
The  white  bands  are  known  as  Baillarger'  s  stripes.  The  corte.x 
of  the  occipital  lobe,  particularly  around  the  calcarine  fissure, 
exhibits  this  stratification  quite  distinctly.  Here  three  layers  are 
found,  an  outer  and  an  inner  gray  stratum  and,  between  them,  a 
thin    light   band,    the   stripe  of    Vicq  a' Azyr    (Fig.    40),    or,    since 

Gennari  first  described  it,  the  stripe  of  Gennari.  The  explanation  of  this  lamellation 
will  be  given  later  by  the  microscopical  examination  of  the  cerebral  cortex  (page  114). 
[n  consequence  of  the  removal  of  the  upper  part  of  the  hemispheres,  as  already 
suggested,  the  corpus  callosum  comes  plainly  in  view.  The  dorsal  surface  of  this  bridge 
lies  before  us,  while  on  each  side  it  is  separated  from  the  overlying  medial  surface  of  the 
hemisphere  by  the  sulcus  corporis  callosi. 


Fig  40  — Vertical  sec- 
tion through  occipital  lobe. 
The  narrow  light  band  is 
the  stripe  of  Gennari. 


40 


MORPHOLOGY. 


The  corpus  callosum,  or  commissura  cerebri  magna,  forms  a  white  medullary 
mass  that  connects  the  hemispheres.  Strands  of  transversely  coursing  fibres,  the  striae 
transve7'sae,  are  seen  on  the  surface  of  the  truncus  or  body  of  the  corpus  callosum. 
They  penetrate  the  wall  of  the  hemispheres  and  form  the  radiatio  corporis  callosi  (Fig. 
39).  The  callosal  radiation  includes  an  anterior,  a  middle  and  a  posterior  part.  The 
anterior  portion,  "Caspars  fj-ontalis,  belongs  to  the  callosal  knee  or  ge7iu  and  connects  the 
anterior  parts  of  the  frontal  lobes.  In  consequence  of  the  frontal  lobes  projecting  beyond 
•  the  genu,  the  connecting  fibres  sweep  in 

curves  far  forward  toward  the  frontal  poles, 
forming  a  sort  of  tongs,  the  forceps  an- 
tcrior.  The  middle  portion,  the  pars 
parietalis,  belongs  to  the  body  of  the 
corpus  callosum  and  unites  the  parietal 
and  temporal  lobes  of  the  two  sides. 
The  posterior  portion  belongs  to  the 
hind  segment  of  the  callosal  body  and 
the  splenium  and,  as  the  pars  temporalis 
and  pars  occipitalis,  connects  the  tem- 
poral and  occipital  lobes.  The  callosal 
fibres  arch  far  backward  toward  the  oc- 
cipital poles  and  form  the  forceps  poste- 
rior. The  induseum  griseiim  covers 
the  upper  surface  of  the  corpus  callosum 
as  a  thin  investment,  that  presents  two 
medial  linear  thickenings,  and,  on  each 
side,  a  lateral  one.  The  medial  longitu- 
dinal stripes,  the  striae  longitudinales  me- 
diales  or  striae  of  Lancisii,  are  separated 
by  a  longitudinal  furrow,  the  raphe  cor- 
poris callosi.  The  lateral  stripes,  situated  within  the  corresponding  sulcus  corporis  callosi, 
are  the  striae  longitudinales  laterales  or  the  teniae  tectae. 

Now  follows  the  opening  of  the  lateral  ventricles.  Such  parts  of  the  hemispheres 
which  still  overlie  the  corpus  callosum  are  removed  as  far  as  the  level  of  the  dorsal  sur- 
face of  the  callosum.  On  separating  these  parts  with  the  fingers,  in  properly  hardened 
brains,  it  is  possible  to  demonstrate  the  radiatio  corporis  callosi,  especially  the  forceps 
anterior  and  posterior.  A  pointed  knife  is  now  passed  through  the  roof  of  the  lateral 
ventricle,  at  the  side  of  the  body  of  the  callosum  and  from  1-2  cm.  behind  the  genu. 
The  incision  is  lengthened  straight  forward  as  far  as  the  level  of  the  genu  of  the  cal- 
losum and  backward,  in  a  slightly  outwardly  convex  curve,  to  a  point  behind  the 
splenium.  By  gradually  widening  the  opening  medially  and  laterally  the  ventricle  is 
exposed. 

THE   LATERAL   VENTRICLE. 

In  each  lateral  ventricle  we  distinguish  three  outpouchings  or  horns,  the  cornu  ante- 
rius ,  the  cornu  posterius  and  the  cortiu  inferius,  invading  the  frontal,  occipital  and  temporal 
lobf.s  respectively,  and  the  middle  chief  part  or  body,  xhe  pars  centralis,  uniting  the  three  horns. 


Fig.  41. — Horizontal  section  at  the  level  of  the  corpu 
callosum.  The  heavy  lines  within  the  centrum  semiovale  indi 
cate  the  incisions  made  in  opening  the  lateral  ventricles. 


LATERAL    VENTRICLE. 


41 


The  front  horn,  the  cornu  anterius,  is  bounded  in  front,  partly  below  and  above 
by  the  fibres  of  the  corpus  callosum.  The  radiation  of  the  callosal  knee  closes  the  ante- 
rior horn  in  front  and  in  addition  forms  a  part  of  the  floor.  The  medial  wall  and,  at 
the  same  time,  the  partition  between  the  two  anterior  cornua  are  contributed  by  the  sep- 
tum pellucidum.  The  latter  consists  of  two  thin  plates,  the  laminae  scpti  pelhicidi,  between 
which  lies  the  completely  closed  caviim  septi  pellucidi.  A  part  of  the  floor  and  the  lateral 
wall  of  the  anterior  horn  are  formed  by  a  gray  protuberance,  the  corpus  striatum.  The 
thickened  front  part  of  the  latter,  which  projects  into  the  anterior  horn,  is  known  as  the 


Corpus  caUosum    __ 


Part  cei:tral!s 


Inferior  horn  (Fmi- 
nentia  coUnteralis) 


Posterior  liorn 


Sulc.   mt,-rmeJ.  (.Stria 
ifrttiiitnlis) 


clps,  viewed  from  abo 


head,  or  caput ;  passing  backward,  the  striatum  markedly  narrows  and,  as  a  narrow 
tail-like  band,  the  cauda  corporis  callosi,  continues  through  the  pars  centralis  into  the 
cornu  inferius,   of  which  horn  it  contributes  a  portion  of  the  roof. 

The  pars  centralis  is  a  thin  horizontal  cleft,  roofed  in  by  the  radiation  of  the 
callosum.  On  the  floor,  laterally,  is  the  corpus  striatum  ;  next  follows  the  stria  termi- 
nalis  or  stria  cornea.  This  structure  forms  the  floor  of  a  groove,  the  sukus  interme- 
dins, situated  between  the  corpus  striatum  and  the  adjoining  thalamus.  The  stripe  is 
called  stria  cornea  on  account  of  its  bluish  coloration,  produced  by  the  underlying  vena 
terminalis.  Medial  to  the  stria  terminalis  comes  a  thin  lamella,  the  lamina  affixa,  that 
covers  the  lateral  part  of  the  thalamus,  to  which  it  is  attached.  P'arther  medially,  follow 
the  plexus  chorioidcus  vcnlriculi  lateralis  and  the  dorsal  surface  of  the  part  of  the  fornix 
which  is  free  and  unattached  to  the  callosum. 

Regarding  the  plexus  chorioideus,  it  must  be  esijccially  emphasized  that  this  struc- 
ture, composed  of  pial  tissue,  really  only  seemingly  lies  within  the  lateral  ventricle.  As 
in  ail  other  parts,  so  also  here  the  ventricle  is  lined  with  ependyma  which  invests  the 
choroid  ple.xus  with  a  thin  epithelial  layer,  the  lamina  chorioidea   epitlulialis  ;  the  ])k'.\us 


42  MORPHOLOGY. 

lies,  therefore,  extraventricular.  Laterally  the  lamina  chorioidea  begins  at  the  lamina 
affixa ;  medially  it  is  continuous  with  the  epithelium  covering  the  fornix  (Fig.  63). 
On  removing  the  plexus  chorioideus,  the  lamina  chorioidea  epithelialis  is  taken  away 
with  it,  the  epithelial  layer  tearing  through   the   medial  border  of   the  lamina  affixa  and 

Lattima  chorioidea  eftr'tli^liolls  zietitriciili  tertii 


Lavtina  chorioidea 

epjtkelinlis  ventr.  laiernl 


Fissura  chorioidea. 


Fig.  43. — Frontal  section  of  the  brain  of  a  human  embryo  of  50  mm.  In  the  middle  are  the  thalami,  with  the  third 
ventricle  (III),  whose  roof  is  formed  by  the  lamina  chorioidea  epithelialis  ventriculi  tertii.  On  each  side,  lateral  to  the 
thalamus,  is  the  hemisphere-vesicle  with  the  lamina  chorioidea  epithelialis  of    the  lateral  ventricle  (II). 

along  the  lateral  border  of  the  fornix.  In  these  locations  delicate  white  stripes,  called 
taeniae,  mark  the  lines  of  separation  ;  hence,  the  taeyiia  chorioidea  and  the  taenia 
fornicis  are  distinguished. 

These  taeniae,  evidently,  as  such  do  not  exist  in  the  normal  and  undamaged 
brain  ;  they  are,  therefore,  artefacts  as  are  also  the  taenia  fimbriae,  taenia  thalami  and 
taenia  ventricidi  quarti,  to  be  described  later.  Their  true  relations  are  to  be  under- 
stood only  by  reference  to  embryology.  While  the  original  wall  of  the  embryonic 
brain-tube  for  the  most  part  thickens  during  development  and  becomes  nervous  sub- 
stance, in  certain  places,  namely  in  the  roof  of  the  third  and  of  the  fourth  ventricle  and 
along  a  band-like  area  on  the  medial  wall  of  the  hemisphere,  such  conversion  into 
nervous  tissue  never  occurs,  the  brain-wall  there  being  represented  by  only  a  thin  epi- 
thelial plate,  the  lamina  chorioidea  epithelialis.  Where  the  latter  joins  the  typical  wall, 
the  nervous  substance  is  thinned  out  to  a  slender  wedge. 

The  lamina  chorioidea,  moreover,  at  certain  places  undergoes  a  complicated  invagi- 
nation toward  the  cavity  of  the  ventricles,  accompanied  by  the  superimposed  pial  tissue,  the 
process  leading  to  the  formation  of  the  plexus  chorioidea.  When  later  the  brain-membranes 
are  removed,  as  when,  for  example,  the  plexus  of  the  lateral  ventricle  is  taken  off,  the 
epithelial  lamina  is  also  removed  and  there  remain  only  dehcate  linear  borders,  known 
as  the  taeniae,  that  mark  the  torn  edges  along  those  lines  at  which  the  brain-substance 
joins  the  epithelial  plate. 


LATERAL    VENTRICLE. 


43 


The  plexus  chorioideus  ventriculi  lateralis  passes  forward,  beconiing  more  deeply- 
placed,  toward  the  anterior  cornu.  Here  is  found  the  Y-shaped  foramen  interventricu- 
lare  Monroi,  which  connects  the  two  lateral  ventricles  with  each  other  and  with  the 
third  ventricle.  Behind,  the  choroid  plexus  continues  outward  and  downward  into  the 
inferior  cornu. 

The  hind  horn,  the  cornu  posterius,  forms  a  narrowing  cleft  of  variable  length, 
with  convex  lateral  and  concave  medial  arched  walls.  The  lateral  superior  wall  is  formed 
by  the  fibre-radiation  of  the  corpus  callosum  ;  the  remaining  boundaries  are  contributed 
by  the  medullary  portion  of  the  occipital  lobe.  On  the  medial  wall,  usually  two  longi- 
tudinal ridges  project  into  the  ventricle.  The  upper  and  less  constant  ridge  is  the 
bulbus   cornu  posterius,    and  is  due   to   the   laterally  arching   callosal    fibres — the   forceps 


—   Gyrus  dentnttis 

Sulcus  fimbriodentatus 


Fig.  44. — Relations  of  the  gyrus  dentatus  (red),  the  fimbria  and  the  for 


,  (yellow). 


posterior,  which  here  curve  around  the  deeply  incising  fissura  parieto-occipitalis.  The 
lower  and  constant  ridge  is  the  calcar  avis  and  owes  its  existence  to  the  deep  penetra- 
tion of  the  fissura  calcarina. 

The  lower  horn,  the  cornu  inferius,  curves  downward  and  far  forward  in  the 
temporal  lobe,  to  end  blindly  before  reaching  the  tip.  The  roof  is  formed  laterally  by 
the  callosal  radiation  known  as  the  tapetum,  medially  by  the  cauda  corporis  striati  and 
the  stria  terminalis.  The  floor  exhibits  the  eminentia  collateralis ,  a  longitudinal  ridge 
produced  by  the  deep  invagination  of  the  fissura  collateralis.  Behind,  toward  the  pos- 
terior horn,  the  eminence  continues  into  a  triangular,  slightly  convex  field,  the  trigoiimn 
coUaierale.  The  medial  wall  of  the  inferior  horn  is  occupied  by  a  remarkable  semilunar 
curved  protuberance,  the  hippocampus  or  cornu  A»imo7iis,  for  whose  production  the  deep 
fissura  hippocampi  is  responsible.  It  begins  behind  the  pars  centralis  or  body  of  the 
lateral  ventricle,  in  advance  of  the  front  end  of  the  calcar  avis,  and  extends  in  a  laterally 
convex  cur\'e  downward  and  forward.  Towards  the  anterior  extremity  of  the  inferior  horn, 
the  hippocampus  broadens  and  then  ends  in  several  claw-like  elevations,  the  digitalioncs 
hippocamfri ,  which  vary  in  development,  in  some  cases  being  merely  suggested,  while  in 
others  they  may  number  four  or  five  or  even  seven.  The  indentations  lying  between 
the  digitations  are  called  the  sulci  interdigitales.  The  marginal  portion  of  the  fornix, 
unattached   to   the  corpus  callosum,   the   dorsal  surface   of   which  has  been  mentioned  in 


44 


MORPHOLOGY. 


relation  with  the  pars  centralis  of  the  lateral  ventricle,  continues  backward  and  outwards; 
it  accompanies  the  hippocampus  medially  into  the  inferior  horn.  The  plexus  chorioideus 
ventriculi  lateralis,  which  is  directly  prolonged  from  the  pars  centralis  into  the  inferior 
horn,  where  it  forms  part  of  the  medial  boundary,  is  especially  well  developed — gloniits 
cko7'ioideum — at  the  juncture  of  the  pars  centralis  and  the  inferior  cornu.  If  the  plexus 
be  separated  from  the  fimbria,  a  thin  lamina,  the  taenia  Jimb7'iae,  remains.  At  its  front 
end,  the  wall  of  the  inferior  horn  constitutes  a  delicate  occluding  lamella,  which  is 
clothed  with  the  ependyma  and  termed  the  velum  terminate  of  Aeby.  The  fornix  and 
the  hippocampus  now  merit  closer  examination   (Figs.   44,   45  and  46). 

The  fornix  represents  a  paired  structure,  that  extends  in  a  bold  curve  from  the 
uncus  gyri  hippocampi  as  far  as  the  corpora  mamillaria.  From  the  inferior  horn  of  the 
lateral  ventricle  on  each  side,  the  fimbria,  at  first  narrow,  extends  backward  toward 
the  splenium  and  here  passes  into  the  posterior  limit  of  the  fornix,  the  crus  fornicis, 
which  runs  forward  beneath  the  callosum.      The  two  crura  fornicis  with  the  under  surface 


Cornu  infi 


Alveus  hippocamp. 


Gyrus         I 
hippocampi  { 


Fig.  45. — Frontal  section  through  the  inferior  ho 
right.     Ependyma  is 


Plexns  chorio 

'deiis 

Fhnbria 

Snlcns  Jiinbri 

odeuti 

t„s 

Gyrus  dentni 

,s 

Fiss.  hippoca} 

,pi 

of  the  lateral  ventricle;  free-surface  of  the  gyrus  hippocampi  is  i 
id;  pia  mater  and  plexus  chorioideus  blue. 


of  the  corpus  callosum  form  an  equilateral  triangle,  whose  apex  is  directed  forward. 
The  two  limbs  of  this  triangle  are  connected  by  strands  of  fibres  running  crosswise  and 
constituting  the  fornix  transversus  or  commissura  hippocampi.  The  entire  triangular 
fibre-plate,  also  designated  as  the  psalteriuni  or  lyra  Davidis,  is  often  separated  from 
the  under  surface  of  the  callosum  by  a  small  cleft,  the  cavum  psalterii,  sometimes  mis- 
leadingly  called  Verga's  ventricle. 

The  crura  of  the  fornix,  which  curve  around  the  posterior  parts  of  the  thalami  and 
pass  toward  the  under  surface  of  the  callosum,  by  their  union  form  the  corpus  fornicis. 
In  its  posterior  part,  the  body  is  attached  to  the  corpus  callosum,  while  it  extends  as  far 
forward  as  the  vicinity  of  the  foramen  interventriculare.  The  under  surface  of  the 
fornix  exhibits  a  median  groove,  the  sulcus  fnediatius  fornicis.  In  front,  the  corpus 
fornicis  divides  into  two  anterior  columns,  the  columnae  fornicis,  which,  as  white  cylindrical 
cords,  sweep  downward  in  forwardly  directed  curves,  in  advance  of  the  thalami  and 
behind  the  commissura  anterior,  and  on  each  side  disappear  in  the  hypothalamic  region. 
They  contribute  the  anterior  boundary  of  the  foramen  interventriculare  and  eventually 
end  in  the  corpora  mamillaria. 


THE    HIPPOCAMPUS. 


45 


The  hippocampus  or  cornu  Ammonis  is,  as  already  mentioned,  produced  by 
the  deeply  invaginating  fissura  hippocampi.  These  relations  are  best  understood  by 
examining  a  frontal  section  passing  immediately  behind  the  uncus  gyri  hippocampi  (Figs. 
45  and  46).  It  will  be  seen,  that  the  entire  cortical  formation  is  pushed  in  toward  the 
ventricle  by  the  penetration  of  the  hippocampal  fissure,  thereby  producing,  in  a  sense, 
an  almost  completely  closed  hollow  cylinder,  in  which  lies  the  gyrus  dentatus  as  a  gray 
cord.  The  upper  end  of  the  scrolled  plate  bends  sharply  outward  and  terminates  as  a 
thin  lamella.  This  invaginated  corte.x,  protruding  into  the  ventricle,  is  the  hippo- 
campus. Since  the  latter  at  the  same  time  overlies  the  gyrus  hippocampi,  this  con- 
volution is  also  called  the  subiculum  cornu  Ammonis.     The  white  fibre-layer  coverino-  the 


Pig.  46. — Section  across  the  hippocampal  region;  the  posterior  end  of  the  corpus  callosum  is  viewed  from  in  front 
and  below.  Transition  of  the  alveus  and  the  fimbria  (yellow)  into  the  forni.x.  The  course  of  the  gyrus  dentatus  (red)  is 
seen  behind  the  splcnium  and,  as  the  induseum,  over  the  corpus  callosum. 

ventricular  surface  of  the  invaginated  cortex  is  the  alveus.      At  the  sharp  outward    bend 
of  the  cortical  plate,  the  alveus  becomes  continuous  with  the  fimbria. 

On  following  the  entire  structure  backward  toward  the  splenium  (best  accomplished 
by  making  several  consecutive  vertical  sections  behind  the  uncus),  it  will  be  seen  that 
the  cortical  formation  of  the  gyrus  hippocampi  passes  over  into  the  cortex  of  the  isthmus 
gyri  fornicati  and,  farther  along,  into  that  of  the  gyrus  cinguli.  The  gyrus  dentatus  separates 
from  the  fimbria  and,  as  the  fa.sciola  cinerea,  passes  around  the  splenium  to  continue  over 
the  corpus  callosum  as  the  induseum.  Alveus  and  fimbria  are  prolonged  into  the  fornix, 
the  alveus  going    into   the  m(fdi;il    and   the   fimliria    into    the  later.il    part    of    the    fornix. 


46 


MORPHOLOGY. 


GRAY  MASSES  AND  NUCLEI. 

In  addition  to  the  gray  cortex,  the  substantia  corticalis,  other  definite  gray  masses, 
known  as  the  nuclei  or  ganglia  of  the  end-brain,  are  found  within  the  interior  of  the 
hemispheres.  They  are  the  nucleus  caudatiis,  the  nucleus  lentiformis,  the  clatistncm 
and  the  nucleus  amygdalae,   and  are  constituent  parts   of  the  stem  of  the  telencephalon. 


Fig.  47. — Frontal  or  vertical  section  of   the  brain,  passing  through  the  knee  of   the  corpus  callosun 
latter  is  the  anterior  horn  of  the  lateral  ventricle. 


each  side  of   the 


Nucleus  cnltdatus 


Nucleus  lenticularis 


Fig.  .18. — Model  of  the  corpus  striatum  and  the  thalamus, 
below  they  are  continuous,  elsewhe 


Ctipsvla  interna. 


Jucleus  caudatus   and  lenticularis  are   yellow;    in  front  and 
separated  by  the  capsula  interna. 


The  nucleus  caudatus  forms  the  part  of  the  corpus  striatum  that  has  been 
mentioned  in  connection  with  the  lateral  ventricle.  The  corpus  striatum  is  divided  by 
a  traversing  fibre-mass  into  two  portions,  a  dorsal  and  medial  one,  the  nucleus  caudatus, 
and  a  lateral  one,  the  nucleus  lentiformis.  The  separating  fibre-mass  is  the  capsula 
interna.  The  thickened  front  end  of  the  corpus  striatum,  that  projects  into  the 
anterior  horn  of  the  lateral  ventricle,  and  the  narrow  band,  that  extends  backward 
through  the  pars  centralis  and  into  the  inferior  horn,  belong  to  the  nucleus  caudatus. 
These  are,  therefore,  more  appropriately  called  respectively  the  caput  and  the  cauda 
nuclei    caudati,    than    the    head    and  tail    of   the    corpus  striatum.      The    lateral    edge    of 


CAUDATE    NUCLEUS. 


47 


the  dorsal  surface  of  the  caudate  nucleus  reaches  the  lateral  margin  of  the  lateral 
ventricle,  its  medial  edge  touches  the  stria  terminalis,  and  its  lateral  surface  lies  against 
the  internal  capsule  (Figs.   49  to  52). 


Fig.  49.^Frontal  section  of  the  brain,  through  the  septum  pellucidum,  which  extends  between  the  body  {Corp.  callos.) 
and  the  rostrum  (C.  c.)  of  the  corpus  callosum  and  forms  the  medial  wall  of  the  anterior  horns  of  the  lateral  ventricles. 
The  corpus  striatum  is  partially  divided  by  the  capsula  interna.    CI,  claustrum. 


rontal  section  o(   the  brain,  through   the   tips  of  the  temporal  lobes,     Cc,  corpus   callosum,  lamina   rostralls; 
Co.  comfnissura  anterior;  C,  ext.,  capsula  externa;   CI,  claustrum;  C,  extr.,  capsula  extrema. 


48  MORPHOLOGY. 

The  nucleus  lentiformis,  or  nucleus  lenticulai-is ,  constitutes  a  wedge-shaped  mass, 
whose  base  is  directed  outward  and  the  apex  inward.  It  Hes  lateral  and,  at  the  same 
time,  ventral  to  the  nucleus  caudatus  and  thalamus,  separated  from  the  latter  by  the 
internal  capsule.  In  front  and  ventrally,  the  lenticular  nucleus  is  directly  continuous 
with  the  head  of  the  nucleus  caudatus.  Dorsally,  delicate  gray  stripes  connect  the  two 
nuclei;  hence  the  designation  "corpus  striatum"  applied  to  the  nuclei  conjointly.  The 
nucleus  lentiformis  bounds  the  internal  capsule  laterally  with  its  downward  and  inward 
sloping  medial  surface.  Its  slightly  convex  lateral  surface  is  vertical  and  borders  the 
capsula    externa,     a    thin     white    medullary    lamella     which     is    limited    externally    by    a 


Fig.  51.— Frontal  section  of  the  brain,  passing  through  the  foramen  interventricula 
fornix,  between  which  and  the  corpus  callosura  is  seen  a  part  of  the  septum  pellucidum 
commissura  anterior;  C.  exL,  capsula  externa;  CI.,  claustrum;   C.  exir.,  capsula  extrema. 


jnroi.      Fo,  pillars    of   th 
:.,  nucleus    caudatus;    d 


narrow  scroll-like  sheet  of  gray  substance  known  as  the  clmistrum.  The  ventral 
surface  of  the  lenticular  nucleus  is  horizontal  and,  in  the  middle  part,  continuous 
with  the  cortex  of  the  substantia  perforata  anterior.  Two  thin  medullary  sheets, 
more  or  less  parallel  with  the  lateral  surface,  subdivide  the  lenticular  nucleus  into 
three  segments.  The  outer  one,  the  putamen,  e.xceeds  the  others  both  in  intensity  of 
color  and  size.  The  inner  segments  are  of  paler  color,  smaller,  and  together  form  the 
globus  pallidus. 

In  the  internal  capsule,  which  extends  between  the  nucleus  caudatus  and  the 
thalamus  on  the  medial  side  and  the  nucleus  lentiformis  on  the  lateral  (Fig.  53),  two 
limbs  are  distinguished,   an  anterior  pars  frontalis  capsulae  internae,  between   the  caudate 


THE   INTE^RNAL   CAPSULE. 


49 


Fig.  S2. — Frontal  section  of   the  brain,  passing  through   the  thalamus   and   the  third  ventricle.    C.  ext..  capsula  externa; 
CI.,  claustrum;  C,  exlr.,  capsula  extrema;  //,  tractus  opticus;  m,  corpus  mamiUare. 


Corpus  callosu 


Corpus  cailosum 


Cornu  potUriiiS 


Nucl.  Cauda  tus 


Nucleus  caudatus  (Cauda) 


Fi*;    S3- — Horizontal  section  of  the  brain. 


50  MORPHOLOGY. 

and  lenticular  nuclei,  and  a  posterior  limb,  pars  occipitalis  capsulae  internae,  between  the 
lenticular  nucleus  and  the  thalamus.  The  two  limbs  meet  in  a  laterally  opening  angle 
known  as  the  knee,   the  gemi  capsulae  internae. 

The  claustrum  constitutes  a  broad  flattened  nucleus,  a  narrow  plate  of  gray  sub- 
stance, which  ventrally  is  somewhat  thickened  and,  more  medially,  joins  the  substantia 
perforata  anterior.  Its  medial  surface  is  smooth  and  bounds  the  thin  capsula  externa. 
The  lateral  surface  presents  small  projections  and  borders  a  white  medullary  sheet,  the 
capsula  extrema,   between  the  claustrum  and  the  cortex  cf  the  island. 

The  nucleus  amygdalae  lies  beneath  the  lenticular  nucleus  in  the  extreme  anterior 
segment  of  the  temporal  lobe.  It  is  continuous  with  the  cortex  of  the  gyrus  hippo- 
campi and  of  the  substantia  perforata  anterior. 

SUMMARY   OF   THE  TELENCEPHALON. 

The  telencephalon,  or  end-brain,  forms  the  most  anterior  and  largest  division  of  the 
encephalon  and  comprises  the  honisphaerium,   and  the  pars  optica  hypothalami. 

A.  The  hemisphaerium  includes  : 

The  pallium  or  the  cerebral-mantle, 

The  rhinencephalon  or  the  olfactory  brain, 

The  stem  of  the  end-brain. 

The  two  hemispheres,  separated  from  each  other  by  the  fissura  longitudinalis  cer- 
ebri, are  connected  by  the  lamina  terminalis,  the  corpus  callosum,  the  commissura  anterior 
and  the  fornix  transversus. 

The  pallium  exhibits  the  cerebral  lobes  and  convolutions,  separated  by  the  inter- 
vening clefts  and  furrows.  As  fissures  or  total  furrows  are  designated  those  deeply 
incising  chief  furrows,  which  are  early  developed  and  which,  in  consequence  of  their 
deep  penetration,  push  in  the  wall  of  the  ventricle.  To  these  belong :  the  fissura  cerebri 
lateralis,  the  fissura  parieto-occipitalis,  the  fissura  calcarina,  the  fissura  coUateralis  and 
the  fissura  hippocampi.  At  the  bottom  of  the  fissura  cerebri  lateralis  lies  the  fossa  cer- 
ebri lateralis,  which  in  a  measure  corresponds  to  a  ventricular  protrusion  of  the  corpus 
striatum.  The  fissura  parieto-occipitalis  corresponds  to  the  bulbus  cornu  posterioris,  the 
fissura  calcarina  to  the  calcar  avis,  the  fissura  coUateralis  to  the  eminentia  coUateralis, 
while  the  fissura  hippocampi  is  responsible  for  the  production  of  the  hippocampus  within 
the  inferior  horn. 

As  sulci  or  cortical  furrows  are  designated  the  less  deeply  penetrating  grooves 
which  are  confined  more  to  the  surface  of  the  hemisphere. 

The  chief  divisions  of  the  cerebral  mantle  are  :  the  lobus  frontalis,  the  lobus  parie- 
talis,  the  lobus  temporalis,  the  lobus  occipitalis  and  the  insula.  The  latter,  however, 
strictly  regarded,  does  not  belong  to  the  cerebral  mantle,  but  to  the  trunk  of  the 
end-brain. 

The  rhinencephalon  falls  into  the  peripheral  and  cortical  regions. 

The  peripheral  region  comprises  the  lobus  olfactorius,  which  in  turn  is  subdivided 
into  the  lobus  olfactorius  anterior  and  posterior. 


SUMMARY    OF   TELENCEPHALON.  51 

The  lobus  ol/actorins  anterior  includes  : — 

The  bulbus  olfactorius, 
The  tractus  olfactorius, 
The  tuberculiim  olfactorium, 
The  area  parolfactoria  of  Broca. 

From  the  tuberculum  olfactorium  the  gyrus  olfactorius  lateralis  extends  laterally 
toward  the  fossa  Sylvii,  here  forms  the  angulus  gyri  olfactorii  lateralis,  then  runs  back- 
ward and  ends  as  the  gyrus  semilunaris  and  gyrus  ambiens  at  the  front  border  of  the 
gyrus  hippocampi.  The  gyrus  olfactorius  medialis  extends  medially  from  the  tuberculum, 
its  continuation  forming  on  the  medial  surface  of  the  hemisphere  the  area  parolfactoria 
of  Broca,   which,   in  turn,   is  prolonged  upward  into  the  gyrus  cinguli. 

The  lobus  o/fadorius  posterior  claims  the  substantia  perforata  anterior  and  the  diag- 
onal band  of  Broca,  which  latter  passes  into  the  gyrus  subcallosus,  situated  on  the  medial 
aspect  of  the  hemisphere  behind  the  area  parolfactoria. 

The  cortical  region  has  as  its  chief  components  :  — 

The  g^Tus  fornicatus,  made  up  of  the  gyrus  cinguli  and  the  gyrus  hippocampi 
with  the  connecting  isthmus. 

The  hippocampus  or  cornu  Ammonis,  pushed  into  the  inferior  horn  of  the  lateral 
ventricle  by  the  hippocampal  fissure. 

The  gyrus  dentatus. 

The  gyrus  uncinatus,  the  gyrus  intralimbicus,  the  gyrus  fasciolaris  and  the  rudi- 
mentary callosal  convolutions  or  gyri  Andreae  Retzii.  Concerning  the  connections  of 
the  peripheral  and  central  regions  consult  pages  145-149. 

The  stem  of  the  end-brain  has  as  its  most  important  part  the  corpus  striatum, 
which  is  separated  by  the  capsula  interna  into  the  medially  situated  nucleus 
caudatus  and  the  laterally  placed  nucleus  lentiformis.  The  latter  is  subdivided  by  the 
medullary  laminae  into  the  putamen  and  the  globus  pallidus.  To  the  stem  of  the 
end-brain  belong,  further,  the  claustrum,  separated  from  the  nucleus  lentiformis  by  the 
capsula  externa,  and  the  nucleus  amygdalae,  located  in  the  extreme  front  part  of  the 
temporal  lobe.  All  these  nuclei  are  connected  with  the  cortex  of  the  substantia 
perforata  anterior. 

Within  each  hemisphere,  the  lateral  ventricle  expands  into  its  three  horns,  the 
anterior,  posterior  and  inferior,  and  the  uniting  body  or  pars  centralis.  The  two  lateral 
ventricles  communicate  with  each  other  and  with  the  third  ventricle  through  the  foramen 
interventriculare  or  foramen  of  Monro. 

B.  The  pars  optica  hypothalami  includes : — 

The  lamina  terminalis. 

The  chiasma  opticuni,   with  the  tractus  optici. 

The  tuber  cinereum. 

The  infundibulum. 

The  hypophysis. 


52 


MORPHOLOGY. 


DIENCEPHALON. 

To  the  diencephalon,  sometimes  called  the  inter-brain,  on  account  of  its  position 
between  the  end-  and  the  mid-brain,   belong  : 

The  thalamencephalon  and  the  pars  mamillaris  hypothalami. 

The  diencephalon  surrounds  the  third  ventricle.  The  immediate  roof  of  the  latter 
is  formed  by  the  la^nina  chorioidea  epithelialis  and  the  tela  chorioidea  ventriculi  tertii, 
which  lies  above  and  fused  with  the  epithelial  sheet.  As  secondary  coverings,  over  the 
tela,  follow  the  fornix  and  the  corpus  callosum. 

The  dissection  of  the  brain  proceeds  in  the  following  manner,  the  display  of  the 
fornix  being  next  undertaken.  To  this  end,  the  callosum  is  cut  through  transversely, 
from  I  to  2  cm.  in  advance  of  the  posterior  border  of  the  splenium.  This  is  best 
accomplished  by  passing  the  knife,  from  the  side  and  horizontally,  above  the  crus 
fornicis  and  then  cutting  through  the  corpus  callosum  from  below  upward  and 
somewhat  obliquely  backward.  The  callosum  is  now  pulled  up,  its  attachment  to 
the  psalterium  severed,  and  separated  from  the  body  of  the  fornix  and,  farther 
forward,  from  the  upper  border  of   the  septum  pellucidum. 


Corpus  callosuv! 
Cornit  anterius 


Cavutn  septi  pellncidi 
Lamina  septi  pellncidi 
Nncl.  caiidatlts 
Stria  temtinalis 


Corpiis  fo: 
Lamina  a/fixa. 
Hippocampus 
Cries  fornicis 
Plexus  chorioid. 
Eminentia  collateralis 
Calcar  avis 
Bnlbus  cc 


—  Cerebellum 


Fig.  54. — Lateral  ventricles  exposed  by  removal  of  the  corpus  callosum. 


After  removal  of  the  corpus  callosum  it  is  to  be  noted,  how  on  each  side  the  fim- 
bria ascends  from  the  inferior  horn  and  passes  into  the  crus  fornicis,  how  the  crura 
fornicis  approach  each  other  and  meet  to  form  the  corpus  fornicis,  and  how  the  columnae 
fornicis  bend  downward  in  front  of  the  foramen  interventriculare  (Fig.  54).  Further  to 
be   observed   are   the   partition   separating   the   lateral  ventricles,  the   septum    pellucidum, 


TELA   CHORIOIDEA. 


53 


with  the  cavum  septi  between  its  laminae,  and  the  course  of  the  plexus  chorioideus 
ventriculi  lateralis  from  the  inferior  horn  through  the  pars  centralis  as  far  as  the 
foramen  interventriculare.  By  means  of  a  probe  or  bristle  may  be  readily 
demonstrated  the  manner  in  which  the  two  lateral  ventricles  are  connected  by  the 
foramen  of  Monro.  The  latter  marks  the  position  at  which  the  plexus  chorioideus 
ventriculi  lateralis  is  continuous  with  the  choroid  plexus  of  the  third  ventricle.  It 
must  not  be  forgotten,  however,  that  the  plexus  really  lies  extraventricular.  On 
removing  the  choroid  plexus,  the  taenia  chorioidea  and  the  taenia  fornicis  are 
recognizable,  and,  likewise,  the  anterior  part  of  the  thalamus. 


chorioidea 
cerebri  int. 


I  'etca  cerebri  jnagna 
(Caieni) 


-Lateral  ventricle 


ventriculi  tertii 


Beneath  the  fornix  lies  the  tela  chorioidea  ventriculi  tertii  (Fig.  55).  In  order  to 
exhibit  the  latter,  we  proceed  in  the  following  manner :  one  peduncle  of  the  fornix  is 
lifted  and  sectioned  with  a  sharp  knife  medialward  and,  at  the  same  time,  obliquely 
backward,  the  section  being  continued  through  the  hind  end  of  the  corpus  callosum, 
thus  cutting  across  the  pars  occipito-temporalis  of  the  radiatio  corporis  callosi.  A 
similar  section  is  executed  on  the  other  side.  The  posterior  end  of  the  callosum  is  now 
raised  and  turned  forward,  with  the  fornix.  The  latter  is  cut  oB  at  the  posterior  margin 
of  the  septum  pellucidum,  where  the  corpus  fornicis  passes  into  columnae  fornicis.  After 
removal  of  the  fornix,  the  tela  chorioidea  lies  free,  beneath  which  the  lamina  chorioidea 
epithelialis  alone  remains  as  the  roof  of  the  third  ventricle.  The  removal  of  the  tela 
chorioidea  is  carried  out  from  in  front  ;  it  is  raised  behind  the  columnae  fornicis  and 
carefully  reflected  backward.  Compare  Figs.  62  and  63  for  orientation.  We  now  pass 
to  the  consideration  of  the  thalamencephiilon. 


54  MORPHOLOGY.     ^ 

THALAMENCEPHALON. 

The  thalamus  opticus  (Figs.  56  and  57)  presents  an  ovoid  mass  of  gray  sub- 
stance, with  the  thicker  end  behind.  Its  dorsal  and  medial  surfaces  are  free,  while  its 
lateral   and  ventral   ones  are  fused  with  the  neighboring  structures.       The  dorsal   surface 


S6. — Lateral  and  third 


jcposed;    the  tela  chorioide 


is  slightly  convex  and  covered  by  a  thin  layer  of  white  fibres,  the  siraium  zonule.  The 
outer  limit  is  formed  by  the  stria  terminalis,  lodged  within  the  S7ilcus  intermedins ;  the 
medial   boundary   is  a  white   stripe,    the    stria    medullaris,   which    indicates    the    boundary 


Lamina  ajfixa 
Ventricubis  tert. 


Pnlvina 

Corpus  g-ef 

icnlat.  laterals 

Co7-pns  ge 

ticnlat.  viediale 

Corpora 

quadrigevilna 

Fig.  57- — Thalamus,  epithala 


nd  metathala 


Taenia  ihalami 
Massa  hitervtedia 
Stria  ntednllaris 

Stilc7is  chorioldens 

Trigonnm  habennlae 

Habenula 

Comviissura  habenularmn 

Corpus  pineale 

FrenuluTTt 

Nervns  trochlearis 

i'elmn  medullar e  anterins 
ed  from  above. 


between  the  dorsal  and  medial  thalamic  surfaces.  A  furrow,  the  sulcus  cko7'toideus ,  runs 
from  before  backward  and  outward  and  lodges  the  plexus  chorioideus  of  the  lateral 
ventricle  (Fig.  57).      At  its  front  end,  the  dorsal  surface  exhibits  a  small  round  elevation, 


THE   THALAMUS. 


55 


the  tuberculum  anterius  thalami ;  behind  is  a  similar  projection,  the  pulvinar.  The 
stria  meduUaris,  the  medial  boundary,  widens  behind  into  a  triangular  field,  the  trigo- 
num  habenulae.  From  the  latter  proceeds  medially  a  white  fibre-strand,  the  fiaben- 
ula,  which  in  front  joins  with  the  habenula  of  the  opposite  side  to  form  the  comtnissura 
habenidarum,  while  behind  it  passes  into  a  flattened  structure,  the  corpiis  pineale.  Medially 
the  stria  medullaris  is  continuous  with  the  lamina  chorioidea  epithelialis,  over  which 
spreads  out  the  tela  chorioidea.  On  removal  of  the  latter,  the  epithelial  layer  is  sepa- 
rated from  the  stria  medullaris.  There  remains,  however,  along  the  line  of  transition  a 
delicate  border,  the  taeyiia  thalami,  which  behind  adheres  to  the  dorsal  surface  of  the 
habenula  and  the  pineal  body  and  is  continuous  with  the  taenia  of  the  opposite  side. 


Fornix  Foramen   Monr 


Coininissiira  anterior 


Massa  intermedia 


Gyrus  cingiiU 


■  suBcailosns  '  ^  o 


Area  parolfactnria. 
IBroca's  fittd) 


58.— Medi! 


Corpus 
I  sagittal  section  of  the  low 


part  of  the  br; 


The  medial  surface  of  the  thalamus  is  vertical  and  contributes  the  lateral  wall  of 
the  third  ventricle.  Its  lower  limit  is  indicated  by  the  sulcus  hypothalamicus  or  sulcus 
Monroi,  that  leads  from  the  foramen  interventriculare  to  the  entrance  of  the  aquaeductus 
cerebri.  The  median  surfaces  of  the  two  thalami  are  united,  about  the  middle,  by 
the  massa  inlermedia,  often  called  the  middle  co?nmissure.  The  ventral  surface  of  the 
thalamus  borders  on  the  hypothalamus,  the  lateral  surface  on  the  capsula  interna  (Fig.  58). 

Behind  the  commissura  habenularum  lies  the  corpus  pineale,  so  called  on  account  of 
its  resemblance  to  a  pine-cone.  It  extends  from  an  outpouching  of  the  dorsal  brain-wall, 
the  most  posterior  part  of  the  roof  of  the  third  ventricle,  and  is  a  small  unpaired  body, 
■whose  base  is  directed  forward  and  the  apex  backward.  In  its  anterior  part,  at  the  base 
and  between  the  upper  and  lower  lamellae,  lies  the  small  evagination  from  the  third 
ventricle,    termed    the  recessus  pinealis.     The  upper  lamella  is  continuous  on  each  side 


56 


MORPHOLOGY. 


with  the  habenula,  the  commissura  habenularum  forming  the  dorsal  wall  of  the  recess. 
The  lower  lamella  is  prolonged  into  the  posterior  commissure  and  the  quadrigeminal  plate. 
Since  the  lamina  chorioidea  epithelialis  is  attached  to  the  dorsal  surface  of  the  pineal 
body,  a  considerable  pocket  is  left  between  this  surface  and  the  lamina  chorioidea  of  the 
third  ventricle;  this  is  the  recessus  suprapinealis.  Sand-like  granules,  the  brain-sand  or 
acervulus,   are  usually  present  within  the  interior  of  the  pineal  body. 

The  posterior  commissura,  cominissura  cerebri  posterior,  is  a  bundle  of  trans- 
versely coursing  fibres  which  projects  into  the  ventricle  and  ventrally  bounds  the 
entrance  of  the  recessus  pinealis.  Its  ventral  surface  defines  the  aditus  ad  aquae- 
ductum  cerebri.  The  commissure  is  best  seen  when  the  posterior  wall  of  the  third 
ventricle  is  viewed  from  in  front  (Fig.   59). 


stria  inedidlarii 
Taenia  thala 


Corpits  pineale 

Covunissnra  posterlo 
III.   Ventricuhis 
Massa  ijiUrniedta 

wall  of  the  third  ventricle,  viewed  from  in  front. 


Turning  to  the  region  behind  the  thalamus,  two  small  protuberances,  the  corpora 
geniculata,  are  to  be  noted  as  additional  parts  belonging  to  the  thalamencephalon.  On 
following  the  tractus   opticus  in   its   course   backward  around   the   cerebral  peduncle,    two 


Peduncichts  cereb. 


Pic.  60. — Course  of  the  tractus  opticus  ; 


Thalaimis 
,ll —  Corp.  gentculat.  7?iedtnU 
Corp,  getilcitlat.  laierale 

Tract,  opticus 


nd  the  cerebral  peduncles  toward  the  corpora  geniculata. 


protuberances  are  encountered — the  elongated  oval  corpus  getiiculatutn  mediale  and  the 
corpus  geniculatum  laterale.  The  latter  is  a  small  elongated  elevation  at  the  hind  and 
lower  end  of  the  thalamus,  lateral  to  the  pulvinar.  The  medial  body  is  separated  from 
the  lateral  body  and  the  pulvinar  by  a  deep  furrow. 


PARS   MAMILLARIS   HYPOTHALAMI. 

The  pars  mamillaris  hypothalami  comprises  the  corpora  mamillaria.  These,  also 
known  as  the  corpora  ca7idicantia,  are  two  round  or  oval  relatively  prominent  projections  on 
the  basal  surface  of  the  brain,  between  the  tuber  cinereum  and  the  substantia  perforata 
posterior.  While  separated  from  each  other  by  a  deep  median  cleft,  their  opposed  surfaces 
are  closely  pressed  together  (Fig.  15).      Although  the   boundaries  of  the  mamillary  bodies 


THE   THIRD    VENTRICLE. 


57 


Fig.  6i.— Part  ,.i  ;h.  lasal  sur- 
face of  the  brain,  showing  the  striae 
albae  tuberis.     {Relzius.) 


are  sharp  medially,  in  front  and  behind,  antero-Iaterally  each  knob  is  continued  into  a  narrow 
stalk  directed  toward  the  substantia  perforata  anterior.  This  stalk,  the  brachmm  corporis 
mann/laris,  is  always  present,  although  variably  developed, 
sometimes  being  broad  and  at  other  times  narrow. 
Occasionally  an  additional  small  lateral  projection,  the 
tuberculum  maniillare  laterale,  is  present,  showing  with 
especial  distinctness  when  it  is  bounded  by  a  small  furrow 
medially  as    well  as  laterally. 

Further,  to  be  mentioned  is  the  stria  alba  luberis  of 
Lenhoss6k.  This  is  a  delicate  white  band,  scarcely  one 
millimeter  in  width,  that  springs  with  fine  converging  fibres 
at  the  hind  slope  of  the  mamillary  body,  runs  forward,  traverses 
the  tuber  cinereum  obliquely  forward  and  outward,  and, 
finally,  disappears  beneath  the  optic  tract.  According  to 
Lenhossek,    the  stria  alba    tuberis   is    nothing   more  than  a 

separated  bundle  of  fornix  fibres,  which  here  pass  superficial  to  the  mamillary  body  (Fig.  6i). 
In  several  cases  Retzius  found  the  stria  distinct  only  on  one  side,  while  in  other  cases  it 
was  present  on  both  sides. 

VEXTRICULUS    TERTIUS. 

The  third  ventricle  is  a  median  inpaired  cleft-like  cavity,  that  communicates  in  front 
with  the  lateral  \entricles  by  means  of  the  foramen  interventricidare  or  foramen  of  Monro, 
and  behind  with  the  fourth  ventricle  by  means  of  the  aquaedudus  cerebri  or  Sylvian 
aqueduct.  The  front  wall  is  formed,  in  the  lower  part  by  the  lamina  tert}iinalis,  in  the 
upper  part  by  the  commissura  anterior  and  the  columnae  fornicis,  while  the  back  wall 
is  formed  by  the  commissura  habenularum  and  the  commissura  posterior  (Fig.  58).  The 
side  walls  are  contributed  by  the  medial  surfaces  of  the  thalami  and  of  the  hypothalami, 
separated  by  the  sulci  hypothalamici.  The  floor  of  the  third  ventricle,  in  the  hind  part, 
is  formed  by  the  cerebral  peduncles  and  the  intervening  posterior  perforated  substance; 
in  the  front  part  it  includes  the  corpora  mamillaria,  the  tuber  cinereum,  with  the  infun- 
dibiilum  and  hypophysis,  and  the  chiasma  opticum.  The  immediate  roof  of  the  \entricle 
consists  of  the  lamina   chorioidea  epithelialis,   which  is  fused  with  the  overlying   tela  cho- 

rioidea  ventriculi  tertii,  behind  is  attached  to  the 
dorsal  surface  of  the  habenula  and  of  the  corpus 
pineale,  and  laterally  passes  into  the  stria  medullaris. 
The  tela  chorioidea  ventriculi  tertii,  or 
velum  interpositum,  represents  an  expansion  of 
the  pia  cerebri  between  the  ventral  surface  of  the 
corpus  callosum  and  the  forni.x,  on  the  one  hand, 
and  the  dorsal  surface  of  the  diencephalon,  on  the 
other.  The  tela  in  form  resembles  an  equilateral  triangle,  whose  apex  lies  in  front,  behind 
the  columnae  fornicis,  and  whose  base  is  behind,  beneath  the  splenium  corporis  callosi  (Figs. 
55,  62  and  63;.  It  consists  of  two  laterally  continuous  sheets,  of  which  the  dorsal  one 
is  attached  to  the  under  surface  of  the  callosum  and  the  fornix,  while  the  ventral  one  in 
the    midrlle  overlies   the   lamina   chorioidea  epithelialis   of   the   tliird   ventricle   and    at    the 


Fir,.  62. — Tela  chorioidea  ventriculi  tertii  is  blue. 


58 


MORPHOLOGY. 


sides  covers  the  larger  part  of  the  dorsal  surface  of  the  thalamus.  Laterally,  where  the 
two  sheets  are  continuous,  richly  vascular  villi-like  tufts  of  the  dorsal  sheet  project  into 
the  lateral  ventricle  to  constitute  the  plexus  chorioideus.  Similarly,  villi  from  the  ven- 
tral sheet  project  into  the  third  ventricle,  where  they  appear  as  two  narrow  stripes  close 
to  the  mid-line  and  together  constitute  the  plexus  chorioidea  ventricitli  tertii.  The 
choroid  plexus  of  the  lateral  ventricle  is  inserted  laterally  in  the  lamina  afifixa — taenia 
chorioidea — and  medially  at  the  free  edge  of  the  forni.x — taenia  fornicis.  The  two  stripes 
of  the  plexus  chorioidea  ventriculi  tertii  are  attached  laterally  to  the  stria  meduUaris — 
taenia  ihalami.  The  choroid  plexus  of  the  lateral  ventricles  and  the  band-like  plexus  of 
the  third  ventricle  come  together  at  the  foramen  interventriculare.  Between  the  dorsa! 
and  ventral  sheets  of  the  tela  chorioidea  lies  arachnoidal  connective  tissue.      In  this  run, 


Corpus  cnllositnt 


Taenia  fc 
Plexus  chorioideus  ventriculi 
lateralis 
Stria  termin 


Taenia  thalanil 


Nucleus  caudat. 


-Diagram  showing   the   relations   oi   the   corpus   callosum,  for 
blue;  ependyma,  red. 


in  the  mid-line  and  close  together,  two  veins,  the  venae  cerebri  interyiae,  into  which 
empty  in  front  the  vena  septi  pellucidi,  from  the  septum  pellucidum,  the  vena  terminalis, 
from  beneath  the  stria  terminalis,  and  the  vena  chorioidea,  from  the  choroid  plexus  of 
the  lateral  ventricles.  Behind,  at  the  hind  end  of  the  tela  chorioidea,  the  venae  cerebri 
internae  unite  to  form  the  vena  cerebri  ?nagna  of  Galen  (Fig.   55). 

Certain  outpouchings  of  the  third  ventricle  claim  mention.  Of  these  the  recessus 
suprapinealis,  the  recessus  pinealis,  the  aditus  ad  aquaeductum  cerebri,  the  recessus  in- 
fundibuli  and  the  recessus  opticus  have  been  noted.  In  front,  is  the  recessus  triatigu- 
laris,  between  the  columnae  fornicis  and  the  commissura  anterior  (Fig.   56). 

THE   NUCLEI   OF   THE   DIENCEPHALON. 


The  Thalamus.  The  thalamus  consists  of  three  chief  nuclei,  the  nucleus  anterior, 
tlje  nucleus  medialis  and  the  nucleus  lateralis,  which  are  imperfectly  separated  from  one 
another  by  white  medullary  stripes,   the  laminae  niedullares. 


NUCLEI    OF    THALAMUS. 


59 


The  nucleus  anterior  includes  the  front  and  dorsal  portion  of  the  thalamus  ;  it 
is,  therefore,  also  known  as  the  dorsal  nucleus.  It  penetrates  wedge-like  between  the 
medial  and  lateral  nuclei,  is  covered  dorsally  by  the  stratum  sonale,  and  rests  ventrally 
upon  a  bifurcation  of  the  lamina  medullaris  interna.  The  thickened  front  end  produces 
the  protuberance  on  the  dorsal  surface  of  the  thalamus  known  as  the  tuberculiim  anterius 
or  corpus  album  subrotundum. 

The  nucleus  medialis  is  bounded  laterally  bv  the  lamina  medullaris  interna  and 
medially  by  the  central    gray  substance,   a  sheet   of  gray  matter  which   invests    the   floor 


Fig,  O4. — Frontal  section  of  the  brain,  passing  through  the  third  ventricle.  ThnUimn-^  a,  i.  /.  nucleus  anterior,  internus 
and  lateralis  thalami;  A'c.  nucleus  caudatus;  C.  &.,  corpus  subthalamicum;  //,  tractus  opticus:  P.p..  pes  pedunculi;  7n. 
corpus  mamillare;  A.   hippocampus  or  cornu  Ammonis;  C.exL,  capsula  externa;   CI.  claustrum;   C.  txlr.,  capsula  extrema. 


of  the  third  ventricle  and  the  medial  surface  of  the  hypothalamus  and  also  forms  the 
massa  intermedia  or  middle  commissure.  Anteriorly  the  medial  nucleus  is  closely  con- 
nected with  the  nucleus  anterior,  although  it  does  not  reach  the  front  end  of  the 
thalamus ;  hence,  in  a  series  of  vertical  sections  carried  through  the  brain,  from  before 
backward,  the  medial  nucleus  first  appears  after  the  anterior  nucleus  begins  to  diminish. 
Behind,  the  medial  nucleus  passes  into  the  pulvinar. 

The  nucleus  lateralis,  the  largest  of  the  thalamic  nuclei,  includes  the  ui)[)er  and 
lateral  portion  nl  the  thalamus  and  surrounds,  in  large  part,  the  anterior  and  medial 
nuclei.  Its  medial  boundary  is  formed  by  the  lamina  medullaris  interna  ;  laterally  it  is 
bounded  by  the  jjosterior  limit  o{  the  internal  capsule,   from  which  it  is  separated  by  the 


6o 


MORPHOLOGY. 


lamina  medullaris  externa  and  the  stratum  reticulare.  The  dorsal  surface  of  the  nucleus 
is  covered  by  the  stratum  zonale  and  assists  in  forming  the  dorsal  surface  of  the 
thalamus.  The  lateral  part  of  this  last-named  surface  is  clothed  by  the  ependyma  of 
the  lateral  ventricle  and  contributes  that  portion  of  the  floor  of  the  ventricle  known  as 
the  lamina  affixa  ;  the  medial  part  of  the  same  surface  belongs  to  the  e.xternal  surface  of 
the    diencephalon    and    is    covered    by    the    ventral   sheet    of    the    tela    chorioidea.       The 


Fig.  65. — Frontal  secti^, 
internus  and  lateralis  thalar 
Ammonis;  CI,  claustrum;  .V, 


the  brain,  passing  through  the  subthalamic  region  Thalamus  a,  r.  I,  nucl 
Qucleus  ruber;  5.  n.,  substantia  nigra;  P.  p.,  pes  pedunculi,  //,  tractus  opti< 
deus  caudatus. 


ventral  surface  of  the  nucleus  laterahs  rests  upon  the  regio  hypothalamica.  In  front,  the 
lateral  nucleus  aids  the  anterior  one  in  defining  the  foramen  interventriculare  ;  behind  it 
passes  into  the  pulvinar. 

The  lamina  medullaris  externa  covers  the  entire  outer  surface  of  the  lateral 
nucleus  and  in  the  region  of  the  pulvinar  broadens  into  a  triangular  medullary  area, 
known  as    Wernicke' s  field  CFig.  207 J. 

The  stratum  reticulare,  or  the  lattice  layer,  forms  the  real  outer  limit  of  the  thalamus 
and  constitutes  a  thin  lamella  of  gray  substance  that  invests  the  entire  outer  surface  of 
the  lateral  nucleus  and  of  the  pulvinar,  separating  the  latter  from  the  internal  capsule. 

As  special  nuclei  of  the  thalamus  are  to  be  noted  the  centrum  medianum  and  the 
nucleus  semilunaris,  the  latter  being  also  known  as  the  corpus  patellare. 

The  centrum  medianum  (Luys)  belongs  to  the  nucleus  medialis  and  presents 
a  rounded  mass  of   gray  substance  that  is  lodged  between   the  medial   and   lateral  nuclei 


SUBTHALAMIC    REGION. 


6i 


and  the  pulvinar.  Laterally  it  is  bounded  by  the  lamina  medullaris  interna,  medially 
it  blends  with  the  nucleus  medialis  (Fig.   207). 

The  nucleus  semilunaris  (Flechsig)  belongs  to  the  nucleus  lateralis,  in  whose 
ventral  part  it  lies,  and  leans  against  the  centrum  medianum  in  the  form  of  a  crescent. 

Additional  special  nuclei  of  the  diencephalon  are :  the  mccleus  habenulae  or 
ganglion  habenulae,  within  the  trigonum  habenulae,  and  the  nucleus  corporis  geniculati 
medialis  and  lateralis,  within  the  corresponding  geniculate  bodies. 

Ventral  to  the  thalamus,  the  regio  siibthalamica  or  the  hypothalamus  spreads  out 
between  the  internal  capsule  and  the  central  gray  substance  of  the  third  ventricle. 


Fig.  66. — Frontal  section  of  the  brain,  passing  through  the  pulvinar  and  the  upper  end  of  the  Sylvian  aquaeduct. 
commissura  posterior;  P.  p.,  pes  pedunculi;  .4,  cornu  Ammonis  or  hippocampus. 


Within  each  corpus  mamillare  lie  two  nuclei,  a  larger  round  nucleus  medialis 
and  a  smaller  nucleus  lateralis,  which  arches  around  the  medial  nucleus  and  includes 
the  front  and  outer  part  of  the  mammillary  body  (Fig.  20i).  Close  to  these  two  nuclei, 
at  the  lateral  and  ventral  side  of  the  nucleus  lateralis,  is  found  a  small  nucleus  accessorius. 

The  nucleus  hypothalamicus,  or  corpus  subthalamicum  (Luys),  lies  within 
the  hind  part  of  the  hypothalamus.  This  lentiform  nucleus  lies  beneath  the  nucleus 
lateralis  thalami  and    medially  to  the  globus  pallidus   of   the  lenticular  nucleus  (Fig.  64). 

The  Capsula  Interna.  Let  us  turn  once  more  to  the  internal  capsule.  It  lies 
between  the  nucleus  lenticularis,  on  the  one  side,  and  the  nucleus  caudatus  and  the 
thalamus  on  the  other.  In  frontal  sections,  it  appears  as  a  lamella  of  white  substance  that 
runs  obliquely  from   above  downward    and    inward,   bounded    externally  by   the  lenticular 


62 


MORPHOLOGY. 


nucleus  and  medially  by  the  caudate  nucleus,  the  thalamus  and  the  subthalamic  region 
(Fig.  67).  An  upper  and  a  lower  region  may  be  distinguished  in  the  internal  capsule. 
The  upper  region,  between  the  lenticular  nucleus  on  the  one  side  and  the  caudate 
nucleus  and  thalamus  on  the  other,  is  known  as  the  regio  thalamica  capsulae  inter^iae. 
The  lower  region  lies  between  the  nucleus  lenticularis  and  the  hypothalamus  and  is  the 
regio  siibtlialamica  capsulae  ititernae. 


Fig.  67. — Frontal  section  through  the  brain,  showing  the  continuation  of  the  internal  capsule  into  the  pes  pedunculi  {P.p.)', 
N.  c,  nucleus  caudatus;  CI,  claustrum;   R,  nucleus  ruber;  Py,  pyramidal  tract. 


In  horizontal  sections  (Fig.  68J,  the  internal  capsule  forms,  in  the  region  of  thalamus, 
an  outwardly  opening  angle  with  a  shorter  anterior  limb,  pars  frontalis,  lodged  between 
the  lenticular  and  caudate  nuclei,  and  a  longer  posterior  limb,  pars  occipitalis,  between 
the  lenticular  nucleus  and  the  thalamus.  The  two  limbs  come  together  at  the  knee,  genu 
capsulae  internae.  The  anterior  limb  of  the  capsule  is  also  called  the/ar.f  lenticulo-caudata, 
the  posterior  one  the  pars  lenticulo-thalamica.  The  hind  limb  extends  some  millimeters 
beyond  the   nucleus    lenticularis,    this    part  constituting  the  pa7-s  retrolenticularis . 


SUMMARY    OF    DIENCEPHALON. 


63 


The  relations  are  different  in  horizontal  sections  passing  through  the  subthalamic 
region.  Here,  the  posterior  limb  and  the  pars  retrolenticularis  of  the  internal  capsule 
alone  are  seen,  the  anterior  limb  having  disappeared.      These  relations  are  readily  under- 


Corfus  call, 


NucL  cnudniiis 


Ventrictiltis  tfrt. 


Cloius  p 

nllid. 

Claustrii 

m 

Capsula 

exi 

Capsula 
(Pars  oc 

int. 
cipit.) 

Fig.  68. — Horizontal  section  of  the  brain.      The  internal  capsule 


Kucleus  catidiitiis  {Cauda) 
iclude  two  limbs  and  a  knee. 


Stood,  when  we  recall  that  in  the  front  part  of  this  region  the  nucleus  lenticularis  is 
continuous  with  the  head  of  the  nucleus  caudatus,  from  which  it  follows,  that  in  the 
subthalamic  region  the  anterior  limb  must  disappear  between  the  lenticular  and  caudate 
nuclei  TFig.  ifi). 

SUMMARY    OF   THE    DIENCEPHALON. 

The    diencephalon    or   inter-brain    is  subdivided  into    the  thalamencephalon  and  the 
pars  mamillaris  hypothalami. 

A.  The  thalamencephalon  includes : 
The  thalamus, 
The  epithalamus. 
The  metathalmus. 

To  the  epitha/amics  belong  : 
The  corpus  pineale. 

The  regio  habenulae — trigonum  habenulae,   commissura  habenularum. 
The  commissura  posterior. 

To  the  melathatamus  belong : 
The  corpora  gc-niculrita. 


64  MORPHOLOGY. 

B.  The  pars  mamillaris  hypothalami  includes  the  corpora  mamillaria. 
The  thalamus  consists  of  three  chief  nuclei : 
Nucleus  anterior  or  dorsalis, 
Nucleus  medialis    (+    centrum  medianum), 
Nucleus  lateralis  (  +    nucleus  semilunaris). 

The  lateral  boundary  of  the  thalamus  is  formed  by  the  lamina  medullaris  externa  and 
the  stratum  reticulare.  Medially  the  thalamus  is  covered  by  the  central  gray  substance, 
which  likewise  clothes  the  medial  surface  of  the  hypothalamus  and  forms  the  massa 
intermedia. 

Within  the  trig07ium  habenulae  lies  the  nucleus  or  ganglion  habenulae. 

The  corpora  geniculata  contain  the  nucleus  corporis  geniculati  medialis  and  lateralis. 

Within  the  hypothalamus,  as  special  centres,  are  found  the  nuclei  of  the  corpora 
mamillaria  and  the  nucleus  hypothalamicus,   or  body  of  Luys. 

The  capsula  interna  lies  between  the  nucleus  lenticularis,  on  the  one  side,  and  the 
nucleus  caudatus  and  the  thalamus,  on  the  other.  It  consists  of  an  anterior  limb,  pars 
frontalis  or  pars  lenticulo-caudata,  a  posterior  limb,  pars  occipitalis  or  pars  lenticulo- 
thalamica,  with  the  pars  retrolenticularis,  and  the  genu  capsulae  internae.  In  horizontal 
sections  through  the  hypothalamic  region  the  pars  frontalis  is  wanting. 

The  diencephalon  encloses  the  third  ventricle  which  communicates  with  the  lateral 
ventricles  by  means  of  the  foramen  interventriculare,  and  with  the  fourth  ventricle  through 
the  aquaeductus  cerebri. 

The  boundaries  of  the  third  ventricle  are  as  follows  : — 

Anterior  wall:     Lamina  terminalis, 

Commissura  anterior, 
Columnae  fornicis. 

Posterior  wall:     Commissura  habenularum, 
Corpus  pineale, 
Commissura  cerebri  posterior. 

Lateral  walls  :     Medial  surfaces  of  the  thalami  and  the  hypothalami. 

Floor :     Cerebral  peduncles, 

Substantia  perforata  posterior. 

Corpora  mamillaria. 

Tuber  cinereum,   with  infundibulum  and  hypophysis, 

Chiasma  opticum. 

Roof :     Lamina  chorioidea  epithelialis  ; 

secondarily,   tela  chorioidea  ventriculi  tertii, 
fornix  and  corpus  callosum. 

The  diencephalon,  together  with  the  telencephalon,  constitutes  the  prosencephalon 
or  the  fore-brain.  The  pars  optica  hypothalami  and  the  pars  mamillaris  hypothalami 
together  form  the  hypothalamus. 

The  foregoing  relations  are  presented  in  recapitulation  in  the  following  table  : 


DERIXATIVES    OF   THE    FORE-BRAIN.  65 


3  I  I 

3  n  .S 


JT  3    § 


£     P 


B^'E.     5.0.2.       S        =q5£         Sg| 


O   X 


r.  o  5 
t5  ■:?  a. 
5    c    n' 


E    o    o    o    o 

c    cr   o-   cr    cr 
^   =    c    =    c 


3       w '  ST  G.   3    2.   3 

C;        r*    r*  -.    n     r*    a^ 


5-  si.  = 


66 


MORPHOLOGY. 


MESENCEPHALON. 

The  mesencephalon,  or  mid-brain,  forms  the  smallest  of  the  brain-segments.  Dorsally, 
it  extends  from  the  root  of  the  pineal  body  to  the  posterior  edge  of  the  quadrigeminal 
plate ;  ventrally,  from  the  mammillary  bodies  to  the  front  border  of  the  pons.  It  is  traversed 
longitudinally  by  the  aquaedudus  cerebri  or  Sylvian  aqueduct.  The  dorsal  part  of  the  mid- 
brain includes  the  quadrigeminal  plate,  lamina  quadrigeniina  ;  the  ventral  part  the  cerebral 
peduncles,  pedunculi  cerebri  and  the  substantia  perforata  posterior ;  and  the  lateral  part  the 
brachia  quadrigemina. 

LAMINA    QUADRIGEMINA. 

The  quadrigeminal  plate  stretches  from  the  root  of  the  pineal  body  to  the  front 
end  of  the  velum  medullare  anterius.  By  means  of  a  shallow  median  longitudinal 
furrow    and    one    running   transversely,   the    plate    is   subdivided    into    four  parts,   each    of 

which  appears  as  a  white  hemispherical  ele- 
vation. The  two  front  and  larger  elevations 
are  the  anterior  quadrigeminal  bodies,  the 
colliculi  superiores,  the  two  hind  and  smaller 
ones  are  the  posterior  quadrigeminal  bodies, 
the  colliculi  inferiores.  The  front  part  of 
the  longitudinal  furrow,  between  the  superior 
colliculi,  is  broad  and  forms  the  trigonum 
subpineale,  on  which  the  pineal  body  rests  ; 
it  sometimes  presents  a  slight  elevation,  the 
colliculus  subpinealis.  In  its  hind  part,  the 
furrow  is  bounded  by  two  strands  of  white 
fibres,  which  extend  to  the  velum  medullare 
anterius  and  are  known  as  the  frenula  veli 
medullaris  atiterioris.  Lateral  from  the  root 
of  the  frenulum,  on  each  side  emerges  the 
trochlear    nerve   (Fig.   69). 

Each  colliculus  continues  laterally  into  an 
arm  or  brachium.  From  the  colliculus  supe- 
rior passes  the  brachium  quadrigeminum.  supe- 
rius,  which  runs  as  a  distinct  white  cord  be- 
tween the  thalamus  and  the  medial  geniculate 
body  and  disappears  in  the  vicinity  of  the  lat- 
eral geniculate  body.  The  colliculus  superior, 
brachium  quadrigeminum  superius,  corpus  geniculatum  laterale  and  pulvinar  stand  in  relation 
with  the  tractus  opticus.  From  the  colliculus  inferior  proceeds  the  brachium  quadrigeminum 
inferius,  which  is  broader,  flatter  and  shorter  than  the  upper,  and  disappears  beneath  the 
medial  geniculate  body. 

PEDUNCULI   CEREBRI. 

The  cerebral  peduncles,  with  the  substantia  perforata  posterior,  form  the  ventral 
portion  of  the  mid-brain  and  are  bounded  by  the  optic  tract  in  front  and  by  the  pons 
and   its  peduncles   behind  (Figs.    15  and  75).       Cross-sections   of   the  mid-brain  show  a 


Fig.    69. — The    mesencephalon    and    the    myelencephalon 
dorsal  aspect;  IV  ventricle  partially  exposed. 


CEREBRAL    PEDUNCLES. 


67 


subdivision   of    the  cerebral    peduncle  into  a  ventral  segment,   the  basis  pedunadi,   and  a 
dorsal  area,   the  tegmentum.       Between   these  subdivisions  lies  a  grayish    black   substance 


Ventricuhts  tert. 
Corpus  geniculai.  nted- 

Corpus  genicul.   laieraU 

Trigonum  lemntsci 

Brachiian  pontis 

Brackium  conjunct tviuf! 

Crus  cereBelli  ad  pontein 


Fig.  70. — Dorsal 


Sulcus  mcsencephali 

me  d talis 

s.  iV.  oculomotorii 


Stria  ttiedullari. 
Trigonum  hnbet 
ale 


Corpus  pi> 

Collicuhts  sup. 

ColUculus  in/. 

Feduncjilus  cerebri 

Frenulum  veli  medullar . 
ant 

Velum  medullare  ant 
Fossa  rhomboidea 


■  of  mesencephalon  and  myelencephalon.     Schematic. 


Fig.  71. — Section  through  the  mesencephalo 
Lamina  quadrigemina 


Aguaeductus  Sylvii 


Nucleus  ruber  -  - 


N.  oculomotorius 


Sulcus  mesencephali  medialis 
Pic.  72. — Section  through  the  mesencephalon,  at  the  level  of  the  oculomotor  nucleus  (///). 


in  the  form  of  a  crescent,  the  substantia  nigra  of  Sommering.      Su])erficia]Iy  the  basis  ;nid 
the    tegmentum   are   separated    by  two  furrows,   medially  by  the  sulcus  ncrvi  ocu/oniotcrii 


68 


MORPHOLOGY. 


or  sulcus  meseyicephali  medialis  and  laterally  by  the  sulcus  mesencephall  lateralis.      Dorsally 
the  tegmentum  is  overlaid  by  the  quadrigeminal   plate. 

The  cerebral  peduncles  emerge  from  the  pons  as  robust  striated  columns  and 
extend  divergingly  toward  the  optic  tracts,  beneath  which  they  disappear.  The  course  of 
the  fibre-bundles  is  worthy  of  note.  They  exhibit  an  outward  and  forward  twist  (Fig. 
75).  Between  the  cerebral  peduncles  Vies  the  fossa  interpeduncularis  (Tarini),  whose 
floor  is  formed  by  the  substantia  perforata  posterior,  penetrated  by  numerous  apertures 
for  the  passage  of  blood-vessels.  The  posterior  part  of  the  fossa  deepens  toward  the 
pons  into  the  recessus  posterior,  while  the  anterior  part,  toward  the  corpora  mamillaria, 
sinks  into  the  recessus  anterior.  ,  The  fossa  is  divided  by  a  shallow  median  furrow  into 
two  symmetrical  halves ;  laterally,  toward  the  cerebral  peduncle,  it  is  limited  by  the 
sulcus  nervi  oculomotorii,  from  which  emerge  the  fibre-bundles  of  the  nervus  oculomotorius. 


Trlgonu-m  lemn, 


Nervus  trochlearis 


Brachiiim  conjunctival 
Brachiunt  ponti. 

Medulla   oblongaici 


Fig.  73. — Lateral 


of   the  brain-stem,  showing  tractus  pedu 


pontis.      Schematic. 


A  special  strand  of  fibres,  the  tractus  peduncularis  transversus,  remains  to  be 
noted.  This  springs  from  the  dorsal  surface  of  the  cerebral  peduncle,  between  the 
brachium  quadrigeminum  posterius  and  the  corpus  geniculatum  mediale,  winds  around 
the  peduncle  midway  between  the  optic  tract  and  the  front  border  of  the  pons  and  dis- 
appears in  the  sulcus  nervi  oculomotorii  (Fig.  75).  According  to  Marburg,  the  tractus 
peduncularis  is  identical  with  the  basal  optic  root  present  in  the  lower  vertebrates.  The 
fibres  are  supposed  to  arise  in  the  retina  and  finally  end  in  the  ganglion  ektomamillare 
located  laterally  to  the  corpus  mamillare. 

AOUAEDUCTUS  CEREBRI. 
This  canal,  the  Sylvian  aqueduct,  forms  a  passage,  lined  with  ependyma,  that  con- 
nects the  third  and  fourth  ventricles.  Dorsally  lies  the  lamina  quadrigemina,  ventrally 
the  tegmentum.  In  cross-sections,  where  the  canal  passes  into  either  ventricle,  it  presents 
an  outline  resembling  a  triangle,  with  the  base  directed  dorsally  and  the  apex  ventrally  ; 
in  the  middle,   its  outline  is  varyingly  cordiform  or  elliptical. 


THE    GRAY    MASSES    OF   THE    MID-BRAIN. 

Surrounding  the  aquaeductus  cerebri  is  the  central  gray  substance,  stratum  gris- 
eum  centrale.  At  the  bottom  of  this  stratum,  at  the  level  of  the  superior  colliculi,  lies 
the  octdomotor  nucleus,  which  joins  the  upward  prolongation  of  the  small  nucleus  nervi 
trochlearis  (Figs.  88  and  89).       Lateral,   at  the   edge  of    the  central  gray  substance,    lies 


SUMMARY   OF   MESENCEPHALON.  69 

the  small  nuilcus  radicis  dccendentis'  nervi  trigemini.  The  yiuckus  of  the  posterior 
commissure  and  posterior  longitudinal  bundle  is  located  in  advance  of  that  of  the  oculo- 
motor nerve.  Ventral  and  lateral  to  the  central  gray  substance,  the  formatio  reticularis 
spreads  out.  Between  the  basis  pedunculi  and  the  tegmentum  lies  the  substantia  nigra, 
which  extends  upwards  as  far  as  the  hypothalamus,  while  between  the  substantia  nigra 
and  the  central  gray  substance  is  located  the  red  nucleus,  the  nuclcics  ruber  or  nucleus 
tegmenti,   which  appears  round  in  cross-sections  (Fig.    207). 

As  small  nuclei  of  the  tegmentum,  the  ganglion  dorsale  tegmenti  and  the  ganglion 
profundum  mesencephali  laterale  et  tnediale  are  to  be  noted.  The  ganglion  dorsale  is  a 
small  round  nucleus  lying  behind  the  trochlear  nucleus,  while  the  ganglion  profundum  is 
lodged  within  the  formatio  reticularis,  \'entro-lateral  to  the  nuclei  of  the  oculomotor  and 
trochlear  nerves. 

The  anterior  quadrigeminal  body  is  covered  by  the  stratum  zonale  and  contains  the 
stratum  griseum  colliculi  superioris ;  the  posterior  body  encloses  the  centrally  placed 
nucleus  colliculi  i7iferioris. 

Within  the  posterior  part  of  the  substantia  perforata  posterior,  towards  the  front 
border  of  the  pons,  scattered  ner\-e-cells  constitute  the  ganglion  intcrpeduncularc  of 
Gudden. 

SUMMARY   OF   THE   MESENCEPHALON. 

The  mesencephalon  or  mid-brain  includes  dorsally  the  corpora  quadrigemina,  with 
the  brachia  quadrigemina  and  ventrally  the  pedunculi  cerebri. 

The  superior  colliculi  and  their  brachia,  together  with  the  lateral  corpora  genicu- 
lata,   stand  in  relation  to  the  optic  tracts. 

The  pedunculus  cerebri  is  subdivided  into  the  basis  pedunculi  and  the  tegmentum, 
separated  by  the  substantia  nigra. 

The  chief  gray  masses  are  : — 

The  stratum  griseum  colliculi  superioris, 

The  nucleus  colliculi  inferioris, 

The  stratum  griseum  centrale, 

The  nuclei  of  the  nervus  oculomotorius  and  trochlearis. 

The  small  nucleus  of  the  nervus  trigeminus, 

The  nucleus  of  the  posterior  commissure  and  posterior  longitudinal  bundle. 

The  nucleus  ruber, 

The  substantia  nigra. 

The  smaller  nuclei  are : — 

The  ganglion  dorsale  et  profundum  tegmenti. 
The  ganglion  interpedunculare. 

The  mid-ijrain  is  traversed  by  the  aquacductus  cerebri  or  Sylvian  aqueduct.  This 
narrow  canal  establishes  communication  between  the  third  and  fourth  ventricles. 

The  mesence[)halon  and  the  prosencephalon  together  constitute  the  cerebrum. 


70  .  MORPHOLOGY. 


ISTHMUS  RHOMBENCEPHALl. 

The  isthmus  rhombencephali  forms  the  transition  from  the  mid-brain  to'  rhomb- 
encephalon, which  latter  is  subdivided  into  the  metencephalon  and  the  myelen- 
cephalon. 

To  the  isthmus  belong  the  brachia  conjunctiva,  the  velum  niedullare  anterius  and 
the  trigonum  lemnisci,  which  structures  collectively  constitute  the  dorsal  part  of  the 
isthmus.  Ventral  are  the  cerebral  peduncles.  The  isthmus  surrounds  the  upper  end  of 
the  fourth  ventricle. 

The  brachia  conjunctiva  cerebelli,  crura  cerebelli  ad  cerebrum,  or  superior 
cerebellar  peduncles,  form  two  flattened  cylindrical  columns  that  emerge  from  the  cere- 
bellum. They  embrace  the  anterior  medullary  velum,  converge  forward  and  come  together 
behind  the  quadrigeminal  plate.  At  the  sides,  the  brachia  conjunctiva  border  on  the 
pontile  peduncles,  separated  from  the  latter  by  the  sulcus  lateralis  mesencephali,  which 
runs  at  first  toward  the  corpus  geniculatum  lateralis  and  then  laterally. 

Corpus  pineale 

Collicnlus  sup.   ~^v„_^\.^_^/^^/^^^,^  Fremihim  veli  medullar. 

ColUcuhis  inf.  \      \^       ^yv^.^^^^^'y^    /  AVrs-.  trochlearis 

Fedunculus  cgrehri '         *^  V^^f^j^y^^^  A  Fibrae  arciformes 


Trigonum  Uvtnisci  _L_--f--   1^ — \ \ Velum  medullare  ant 

BracJiiuvi  conjunctlv. 


Fig.  74- — Dorsal  view  of  the  isthmus  rhombencephalon. 

The  velum  medullare  anterius  is  a  thin  medullary  sheet  that  stretches  between 
the  brachia  coniuncti^'a  or  the  superior  cerebellar  peduncles.  Dorsally  it  is  covered  by  and 
fused  with  the  lingula  of  the  cerebellum  and  assists  in  roofing  in  the  anterior  part  of  the 
fourth  ventricle  (Fig.  79).  From  the  narrow  front  end  of  the  velum  arises  \h&  frenulum 
veli  meduUaris  a7iterions  that  extends  toward  the  inferior  colliculi. 

In  advance  of  the  front  end  of  the  brachium  conjunctivum,  lies  a  triangular  field, 
the  trigonum  lemnisci.  It  is  usually  distinguishable  from  the  whiter  brachium  by  its 
gray  color.  Laterally,  the  trigonum  borders  on  the  cerebral  peduncle,  separated  by  the 
sulcus  lateralis  mesencephali,  in  front  it  is  bounded  by  the  brachium  quadrigeminum 
inferius  and  the  inferior  colliculi.  The  area  contains  the  fibre-tracts  of  the  fillet  or  lem- 
niscus and,  deeply  placed,  the  nucleus  lemnisci  lateralis.  Occasionally  one  notes  delicate 
white  fibre-strands  that  pass  from  the  sulcus  mesencephali  lateralis  over  the  brachium,  par- 
ticularly in  the  vicinity  of  the  quadrigeminal  bodies.  Some  of  the  strands  bend  medially 
at  right  angles  and  pass  backward  through  the  anterior  medullary  velum.  These  fibrae 
arcifo7-mes  belong  to  a  bundle  that  ascends  from  the  spinal  cord  to  the  cerebellum,  the 
tractus  spino-cerebellaris  ventralis  or  Gowers'   tract  (page  161). 


PONS   VAROLII. 


71 


METENCEPHALON. 

To  the  metencephalon  belong  the  pons  and  the  cerebellum. 

PONS  VAROLII. 

We  distinguish  a  pars  dorsalis  and  a  pars  basalis  pontis.  The  pars  dorsa/is  corresponds 
to  the  pars  intermedia  of  the  floor  of  the  fourth  ventricle.  The  pars  basa/is  forms  a  broad 
white  bolster,  that  e.xpands  transversely  and  is  bounded  in  front  by  the  cerebral  peduncles 
and  behind  by  the  medulla  oblongata.  The  lateral  boundary  is  indicated  by  a  line  connect- 
ing the  points  of  emergence  of  the  roots  of  the  trigeminal  and  facial  nerves.  Lateral  to  this 
line,  the  pons  narrows  and  passes  on  each  side  into  the  brachium  pontis,  or  middle  cerebellar 
peduncle,  which  extends  backward  and  enters  the  cerebellum.     The  ventral  surface  of  the 

Tracttis  opt: 
Pednnculus  cerebri 


of  the  brain-stera. 


pons  is  arched  in  the  sagittal  and  transverse  directions  and  e.xhibits  a  distinct  transverse 
striation.      These  transverse  fibres  are  grouped  in  three  more  or  less  well-defined  bundles  . 

The  fascicubis  superior  pontis,  which  courses  in  advance  of  the  attachment  of  die 
trigeminal  nerve. 

The  fascicuhis  inferior  pontis,   in  the  lower  third  of  the  pons. 

The  fasciculus  medius  pontis,  between  the  foregoing  bundles,  which  crosses  the 
fasciculus  inferior  in  convex  curves  and  runs  towards  the  places  of  attachment  of  the 
facial  and  acoustic  nerves.  On  account  of  this  course,  the  bundle  is  also  called  the 
fasciculus  obliqims  pontis  or  fasciculus  arcuatus  (Foville). 

The  ventral  pontile  surface  is  modelled  in  the  mid-line  by  a  broad  furrow,  the  sulcus 
hasilaris,  in  which  the  basilar  artery  usually  lies.  This  furrow,  however,  is  not  caused  by  the 
basilar  artery,  but  by  the  two  adjacent  longitudinal  ridges,  the  entinentia  pyramidales,  which 
contain  the  pyramidal  tracts.  The  sulcus  basilaris  is  present  even  when  the  basilar  artery 
pursues  an  irregular  course  ;  it  disappears,  however,  in  degeneration  of  the  pyramidal  tracts. 

The  taenia  pontis  ox  fibra  pontis  is  a  special  band  of  fibres  that  arises  in  or  medial  to  the 
sulcus  mesencephali  lateralis,  runs  along  the  front  border  of  the  pons  and  disappears  in 
the  sulcus  nervi  oculomotorii  ;  these  fibres  are  also  called  the  fila  laieralia  pontis  (Fig.    73). 


72 


MORPHOLOGY. 


THE   CEREBELLUM. 


The  cerebellum,  or  little  brain,  is  a  medially  situated  structure  of  kidney-like  form. 
It  underlies  the  occipital  lobes  of  the  cerebrum_,  from  which  it  is  separated  by  the  large 
transverse  fissure,  and  lies  behind  the  pons  and  the  corpora  quadrigemina  and  above  the 
medulla  oblongata.  We  distinguish  an  upper  and  a  lower  surface  and  an  anterior  and  a 
posterior  border.  Both  surfaces  are  arched  ;  the  under  and  more  strongly  convex  surface 
exhibits  in  the  middle  a  broad  sagittal  depression,  the  vallecula  cerebelli,  in  which  lies 
the  medulla  oblongata.  The  anterior  border  is  indented  in  the  mid-line  by  the  incisura 
cerebelli  anterior ;  likewise,  the  posterior  border  by  the  incisura  cerebelli  posterior.  At 
the  borders  of  the  incisura  are  the  anguli  anteriores  and  posteriores.  Front  and  hind 
borders  meet  in  the  anguli  laterales.  The  median  part  of  the  cerebellum,  lying  between 
the  incisura  anterior  and  posterior,  is  known  as  the  worm,  the  vermis  cerebelli.  The 
ve?-mis  superior  is  defined  from  the  lateral  portions,  the  cerebellar  hemisphei'es ,  by  two 
shallow  furrows,  while  the  vennis  inferior  is  more  sharply  demarcated  by  deeper  grooves. 
The  narrow  convolutions,  gyri  cerebelli,  are  separated  from  one  another  by  numerous 
more  or  less  parallel  fissures,  the  sulci  cerebelli,  particularly  in  the  worm  and  the  hemi- 
spheres. A  deeply  penetrating  fissure,  the  sulcus  horizontalis  cerebelli,  extends  on  each 
side  from  the  entrance  of  the  pontile  arm  or  middle  cerebellar  peduncle  in  the  cerebellum 
along  the  front  border  towards  the  angulus  lateralis  and  thence  toward  the  angulus  pos- 
terior. By  means  of  this  fissure,  each  hemisphere  is  divided  into  an  upper  and  a  lower 
surface,  the  fades  superior  and  fades  inferior.  The  sulcus  horizontalis  is  readily  located 
when  we  pass .  from  the  position  at  which  the  pontile  arm  enters  the  cerebellum.  The 
sulcus  begins  lateral  to  this  location,  at  first  penetrating  but  slightly,  and  is  here  dis- 
tinguished by  the  narrow  convolutions  of  the  upper  and  lower  surfaces  entering  its 
depth.  From  the  lateral  angle,  the  sulcus  proceeds  as  a  deeper  cleft  along  the  hind 
border,  more  on  the  lower  than  the  upper  surface,  toward  the  incisura  cerebelli  posterior. 

The  worm  and  hemisphere  regions  of  the  cerebellum  are  subdivided  into  definite 
lobes  by  certain  more  or  less  deeply  cutting  fissures.  In  each  hemisphere  three  lobes 
are  distinguished  :  lobus  stcperior,  lobus  posterior  and  lobus  hiferior,  the  individual  lobes 
of  the   hemisphere  always  corresponding  to  definite  segments  of  the  worm-region. 

A.  Lobus  Superior.  The  lobus  superior  is  bounded  in  front  by  the  incisura 
cerebelli  anterior,  at  the  side  by  the  sulcus  horizontalis  cerebelli  and  behind  by  the  sulcus 

Lingytia  and   I  incicla  Li?igitla, 


Lohnlns 
q7iaeir(t7t- 
giUaris 


Lobidus  seytiilunaris 
sitfertor 


Lobuliis  semilunaris 


Fig.  76. — Upper  surface  of  the  cerebellum. 


THE    CEREBELLUM.  73 

superior  posterior.  The  sulcus  superior  posterior  starts  in  the  sulcus  horizontalis  somewhat 
in  advance  of  the  lateral  angle  and  passes  as  a  deep  curved  fissure,  directed  posteriorly  with 
its  convexity  toward  the  hind  end  of  the  vermis  superior.  The  sulcus  is  readily  recognized 
by  the  different  relations  of  the  bounding  lamellae,  since  those  of  the  superior  lobe  run 
obliquely  outward  and   forward,   while  the  lamellae  of  the  posterior  lobe  run  parallel. 

Passing  from  before  backward,  the  worm  and  the  hemisphere  present  the  following 
parts  of  the  lobus  superior  : 

WORM  HEMISPHERE 

Lingula Vinculum  lingulae 

Lobulus  centralis Ala  lobuli  centralis 

.     ,       (  Culmen  )  .    ,  ,  ,     .    (  Pars  anterior 

Monticulus  ->  ^     ,.       (- Lobus  quadrangulans  i  ._ 

(  Declive  )  ^  "  (  Pars  posterior 

The  lingula  lies  deeply  placed  in  the  incisura  cerebelli  anterior  and  consists  01 
from  four  to  si.x  or  eight  small  lamellae,  which  rest  upon  and  are  fused  with  the  velum 
medullare  anterius.  Lateral  from  the  posterior  lamellae,  the  vinicula  lingulae  extend 
toward  the  middle  cerebral  peduncle. 

Behind  the  lingula,  and  separated  from  it  by  the  sulcus  praecentralis,  follows  the 
lobulus  centralis,  which  overhangs  the  lingula  and  laterally  sends  out  its  lamellae,  the 
aloe  lobuli  centralis. 

The  monticulus,  the  largest  segment  of  the  superior  worm,  lies  behind  the  lobulus 
centralis,  separated  from  the  latter  by  the  sulcus  postcentralis.  It  includes  the  culmen 
and  the  declive  and  corresponds  to  the  hemisphere-segment  of  the  lobulus  quadrangjclaris. 
The  latter  is  subdivided  by'  the  sulcus  superior  anterior  into  a  pars  anterior  and  a  pars 
posterior,   corresponding  to  the  culmen  arid  declive  respectively. 

B.  Lobus  Posterior.  The  lobus  posterior  includes  the  hind  part  of  the  upper 
surface  and   the   posterior   half  of  the  under  surface   of   the   cerebellum.       It  is   separated 

Nodnlus 


Svle.  prntpyraniidnUs 
SuU.  pottpyrnmidalls 


Uvula 
TonsUle 

Lobulus  biventer 


Pic.  77. — Lower  surfacu  of  the  cerebellu 


from  the  lobus  superior  by  the  sulcus  superior  [josterifjr,  and  from  the  lobus  inferior  by 
the  sulcus  pobtpyramidalis  in  the  worm  and  by  the  sulcus  inferior  anterior  in  the  hemi- 
sphere. The  sulcus  inferior  anterior  may  be  readily  identified  if  the  course  of  the  sulcus 
su[)erior  posterior  be  followed.       It  begins  at  the  side,   on   the   front  border  of  the  hemi- 


74  MORPHOLOGY. 

sphere,  in  the  sulcus  horizontahs  cerebelli  at  the  place  where  the  sulcus  superior  posterior 
opens,  thence  runs  in  a  curve  toward  the  worm,  where  it  ends  in  the  deeply  pene- 
trating sulcus  posipyramidalis . 

By  means  of  the  sulcus  horizontalis  and  the  sulcus  inferior  posterior,  the  posterior  lobe 
of  the  hemisphere  is  subdivided  into  three  parts,  which  correspond  with  two  segments  of 
the  worm. 

WORM  HEMISPHERE 

Folium  vermis Lobulus  semilunaris  superior 

„  ,  .  (  Lobulus  semilunaris  inferior 

Tuber  vermis i  ,    i    i  -i- 

(  Lobulus  gracilis 

The  folium  vermis  lies  in  the  incisura  cerebelli  posterior,  forms  a  single  stout 
lamella  and  connects  the  two  upper  crescentic  lobules,   the  lobuli  semilunares  superiores. 

The  tuber  vermis  or  tuber  valvulae  corresponds  to  the  lobulus  semilunaris  inferior 
and  the  lobulus  gracilis.  The  lobulus  semihmaris  inferior  is  broad  medially  and  narrow 
laterally,  and  often  separated  into  two  parts,  an  anterior  and  a  posterior,  by  a  lateral 
fissure  that  runs  into  the  sulcus  horizontalis.  The  anterior  and  smaller  part  maintains 
approximately  the  same  width  throughout  and  at  the  side  is  aoplied  to  the  lateral  end 
of  the  lobulus  gracilis.  The  posterior  and  larger  part  exhibits  usually  two  or  three  small 
lobules,  often  two  crescentic  segments,  of  which  one  begins  medially  at  the  worm  with 
the  thicker  end  and  ends  laterally  in  a  point,  and  the  other  begins  broad  at  the  side 
and  becomes  pointed  toward  the  worm.  The  lobulus  gracilis  lies  in  front  of  the  lobulus 
semilunaris  inferior,  maintains  a  more  or  less  constant  thickness  throughout,  and  is 
separated  from  the  lobulus  semilunaris  inferior  by  the  sulcus  inferior  posterior  and  from 
the  lobus  inferior  by  the  sulcus  inferior  anterior. 

C.     Lobus  Inferior.     This  lobe  includes  the  following  parts  : 

WORM  HEMISPHERE 

Pyramis Lobulus  biventer 

Uvula Tonsilla 

NoduluS Flocculus  Montla.U, 

Lobulus  centralis 

Lingitla 

Velum  mednlL  ant. 

J    n      „  j^//r  /  j^y.^^--s, — ><r'r'*r*^E?XX_\Vi\  ITv BrachluiH   €0711. 

yelitjn  mednllare   ^w//f>'  ^'^^iy^^jSaittvJ^^y  ^'^WJjYt-."" xj'"^''  j 

iich'mm  pontis 
Nodulus 

Flocculus 

Uvula  VVtltttTTTTT  I  I  1  \  \\  I  \  W^^^^^"-:^^////// ////// 1  \    I  1 1  I  /)|  1  H TmtsUle 

Lobulus  biventer 

Pyramis    -^^R\\C\v\.  \  VvOv!?^^^^^^^^^^^=^^^^<%^^^  ,    ,    ,  •/■ 

Ns>\\\\\\\.   \  \\  \     — ^^x^Jr^~ '<^^^  y  /  ^^^////,y Lobulus  gracilis 

^/j/^ Lobuhis  semilunaris 

y^j^  inferior 


Fig.  78 


The  pyramid,  separated  from  the  tuber  vermis  by  the  sitlcits  posipyramidalis^  connects 
the  biventral  lobule  of  the  one  side  with  that  of  the  other.  A  fissure  splits  each  lobulus 
biventer  into  two  portions,   an  anterior  medial  and  a  posterior  lateral. 


THE   CEREBELLUM. 


75 


The  tonsilla  is  embraced  by  a  medially  concave  curve  described  by  the  sulcus 
praepyramidalis,   which  separates  the  pyramis  from  the  uvula. 

In  advance  of  the  uvula  lies  a  small  conical  structure,  the  nodulus.  Immediately  in 
front  of  the  latter  is  a  thin  white  sheet,  the  velum  iiiedullare posterius,  that  continues  laterally 
on  each  side  as  the  pedunculi  Jlocculi  to  join  the  flocculus.  Lateral  to  the  latter,  between 
the     lobulus     quadrangularis     of 

the  superior  lobes  and  the  lobulus  •^"■'"'■'     ''"'"""  ^'"-•"-    '^'•'"''  ^"''"'^ 

bi\'enter    is    seen    the    accessory 
flocculus,  flocculus  secundarius. 

On  removing  the  tonsil,  a 
broad  lamella,  the  ala  uvulae,  or 
the  furrocced  bmid,  is  seen  pass- 
ing outward  from  the  uvula.  The 
posterior  margin  of  this  band  is 
free,  its  anterior  one  is  continuous 
with  the  posterior  medullary  ve- 
lum. The  deep  recess,  whose  floor 
is  formed  by  the  ala  uvulae  and 
the  velum  medullare  posterius, 
lodges  the  tonsil  and  is  called 
the  nidus  avis.  Its  lateral  wall 
is    contributed     by    the    lobulus 

biventer  and  the  pedunculus  flocculi,  while  it  is  bounded  medially  by  the  uvula  and 
behind  by  the  pyramid.  The  lobulus  biventer  forms  the  lateral,  the  tonsil  the  medial 
and  the  flocculus  the  anterior  part  of  the  lobus  inferior. 

The  foregoing  relations  are  recapitulated  in  the  following  table: 


Lobulus  centralis 


IV.  Ventricitlus 


Pons 

-Median  sagittal  sect 


of   the  cerebellu 


VERMIS  HEMISPHAERIUM 

r  Lingula Vinculum  hngulae 

I       —  Sulcus  praecintralis 

Lobulus  centralis Ala  lobuli  centralis 

Lobus  superior    \       —  Sulcus  postcentralis 

,  _  ,          ^  f  T    u  1              A           {  Psrs  anterior 

,,      .     ,        (  Culmen  )  Lobulus   quadran-    \         „  , 

Monticulus   i  ,,     ,.       \   i  ,     .               <  — Stitc.  sup.  ant. — 

1  Dechve   I  1  gularis  „ 

I  \  ^  y  Pars  posterior 

—  Sulcus  superior  posterior  — 

Folium  vermis Lobulus  semilunaris  superior 

Sulcus  horizontalis  cerebclli  — 

Lobus  posterior  ■]  i    Lobulus  semilunaris  inferior 

Tuber  vermis \        —  Sulcus  inferior  posterior  — 

I    Lobulus  gracilis 

—  Sulcus  postpyramidalis  —  —  Sulcus  inferior  anterior  — 

f  Pyramis Lobulus  biventer 

,    .       •    ,    .         I       —  Sulcus  praepyramidalis 

Lobus  inferior     >   ,,     ,              r      r.r  ^       ... 

uvula Tonsilla 

I  Nodulus Flocculus  ( Flocculus  secundarius) 

On  sectioning  the  cerebellum,  we  recognize  the  internally  situated  white  medullary 
substance,  the  corpus  medullare,  and  the  substantia  corticalis,  which  invests  the  periphery 
as  a  thin  continuous  band  of   gray  matter.       The   medullary  substance  of  the  cerebellum 


76 


MORPHOLOGY. 


is  composed  of  that  of  the  hemispheres  and  of  the  worm,  which  are  continuous  medially. 

Stout    tracts    of    medullary    substance,   the   laminae    medullares,   pass    outward    from    the 

medullary    centre   and    send    off,    mostly    at   acute   angles,    secondary   medullary   laminae. 

The  latter,  in  turn,  give  off  still  smaller  sheets, 
which  finally  are  enclosed  by  gray  substance  and 
represent  the  cerebellar  convolutions  or  folia,  the 
gyri  cerebelli.  This  structure,  when  viewed  in 
sagittal  sections,  is  known  as  the  arbor  medullaris , 
on  account  of  the  tree-like  branching.  In  sagittal 
sections  through  the  worm,  where  this  delicate 
figure  is  particularly  well  seen,  it  is  called  the  arbor 
vitae  vermis. 

The  medulla  of  the  hemispheres  is  con- 
nected with  neighboring  parts  of  the  brain  by 
masses    of     nerve    fibres.      These    masses  constitute 

more  or    less  robust    columns,    which    are    termed    the    peduncles,     crura    or    brachia   of 

the  cerebellum  and    serve    to    connect  it    with  the  pons,   the    mid-brain    and   the    medulla 

oblongata. 

The    brachia    pontis,   middle   cerebellar  peduncles,    or   crura    cerebelli   ad  pontem, 

emero-e    on    each    side   from    the    horizontal    sulcus    at   the   anterior   border,    between    the 


Fig.  8o. — Schematic  representation  of  the 
crura  cerebelli.  Blue,  superior  peduncle;  green, 
middle  peduncle;  yellow,  inferior  peduncle. 


BrachiJim  conjitnctivutH 


Fig.  8i. — Superior  cerebellar  peduncles,  also   termed   crura   cerebelli   ad    corpora   quadrigemina  and  brachia  conjunctiva 
Portion  of  the  cerebellum  has  been  removed  to  expose  the  dentate  nuclei. 


lobulus  quadrangularis,    tonsilla   and    flocculus,   and    pass    convergingly   forward,   to    blend 
with  the  pons. 

The  crura    cerebelli   ad  cerebrum  or  superior  cerebellar  peduncles,    also   known 
as  the  criu-a  cerebelli  ad   corpora   quadrigemina  and  the  brachia  conjunctiva   cerebelli,   lie 


MEDULLA    OBLONGATA. 


77 


in  front  of  the  pontile  crura,  pass  as  flattened  cylindrical  columns  convergingly  forward  and 
disappear  beneath  the  quadrigeminal  bodies.  The  velum  meduUare  anterius  stretches  out 
between  them. 


Tractus  cerebro- 


Brachn 
Ponth 


Fig,  82. — Brachia  pontis 


and  corpora  restiforn 


The  crura  cerebelli  ad  medullam  oblongatam  or  inferior  cerebellar  peduncles, 
also  often  called  the  corpora  restiformia,  pass  out  between  the  foregoing  cerebellar  arms 
and  turn  sharply  backward  and  downward  into  the  medulla  oblongata. 


MYELENCEPHALON. 
MEDULLA   OBLONGATA. 

The  upper  boundary  of  the  medulla  oblongata  is  marked  ventrally  by  the 
inferior  edge  of  the  pons  and  dorsally  by  the  striae  acusticae  in  the  floor  of  the 
fourth  ventricle ;  the  lower  boundary  is  indicated  by  the  attachment  of  the  upper 
root-bundles  of  the  first  cervical  nerves,  or,  ventrally,  by  the  lower  limit  of  the 
pyramidal  decussation. 

Let  us  first  examine  the  ventral  surface  of  the  medulla  (Fig.  75).  In  the  mid- 
line runs  the  fissura  niediana  anterior,  which  is  prolonged  into  the  fissure  of  the  spinal 
cord  bearing  the  same  name,  but  separated  from  it  by  the  crossing  fibre-bundles  of  the 
pyramidal  decussation,  decussatio  pyramidum.  Toward  the  lower  edge  of  the  pons,  the 
fissure  widens  into  a  small  depression,  the  foramen  caecum.  On  both  sides  the  median 
fissure  is  bordered  by  the  pyramid,  a  slightly  convex  tapering  column,  broad  above  and 
narrow  toward  the  spinal  cord,  which  appears  to  pass  into  the  anterior  column  of  the 
cord.  Only  a  small  part  of  the  pyramidal  fibres,  however,  actually  maintains  a  course 
along  the  anterior  median  fissure  in  the  anterior  column  of  the  spinal  cord,  since  the 
greater  part  crosses  the  mid-line  in  the  decu.ssatio  pyramidum  and  continues  within  the 
lateral  column  of  the  cord  of  the  opposite  side.  The  part  which  continues  within  the 
anterior  column  is  known  as  the  anterior  pyramidal  tract,  that  within  the  opposite  lateral 
column  as  the  lateral  pyramidal  tract.  These  will  receive  more  detailed  attention  in  the 
consideration  of  the  fibre-paths  (page   i6r). 


78 


MORPHOLOGY. 


The  pyramid  is  bounded  on  the  outer  side  by  the  sulcus  lateralis  anterior,  from 
which  emerge  the  root-bundles  of  the  hypoglossal  nerve.  Lateral  to  the  sulcus  lateralis 
and  adjoining  the  pyramid  is  seen  the  oliva,  an  ovoid  eminence  whose  thicker  end 
reaches  as  far  as  the  pons  and  which  narrows  below.  The  sulcus  lateralis  anterior  may 
be  marked,  especially  in  its  lower  part,  by  transversely  arching  strands  of  fibres,  known 
as  the  Jibrae  arcuatae. 

Turning  now  to  the  dorsal  aspect  of  the  medulla  (Fig.  83),  we  note,  in  the 
lower  part,  the  sulcus  medianus  posterior,  which  above  is  soon  closed  by  a  thin  medullary 
sheet,   the  obex.       At  this   point,  beneath  the   obex,   the  central  canal  of   the  cord  opens 


Fossa  medlana 


Ventricnl.  Arantii 


Obex 
post. 


Sulc.  > 
Side,  internied.  past. 
Funic,  gracilis     Fun.  cuneat.     Fun.  lateralis  Sulc.  lateral,  post. 

Fig.  S3. — Fossa  rhomboidea,  showing  details  of  the  floor  of  the  fourth  ventricle. 


into  the  fourth  ventricle.  Lateral  to  the  sulcus  medianus,  next  comes  the  sulcus  inter- 
medius  posterior,  which  in  the  upper  part  of  the  medulla  runs  laterally  and  then  disappears. 
Farther  outward  is  the  less  distinct  sulcus  lateralis  posterior,  which  likewise  turns  out- 
ward and  may  be  followed  to  about  the  level  of  the  middle  of  the  olive.  Between  the 
median  and  lateral  posterior  sulci,  the  posterior  column,  funicuhcs  posterior,  represents 
the  upward  prolongation  of  the  corresponding  column  of  the  spinal  cord.  By  means  of 
the  sulcus  intermedius  posterior  the  funiculus  is  subdivided  into  two  special  tracts.  On 
each  side  of  the  posterior  median  fissure,  between  the  latter  and  the  posterior  interme- 
diate fissure,  lies  the  fasciculus  gracilis,  or  Goll' s  coluimi,  continued  upward  from  the 
cord.  In  the  upper  part  it  broadens  into  the  clava  and  then,  again  narrowing,  proceeds 
laterally  and  upward.  Between  the  lateral  and  intermediate  posterior  sulci  runs  the 
fasciculus  cuneatus,  the  upward  prolongation  of  Burdach' s  column,   which  at  the  level  of 


THE    FOURTH    VENTRICLE.  79 

the  clava  expands  into  the  titbcrculum  ciineatum  and  higher  up  also  bends  outward. 
Lateral  to  the  sulcus  lateralis  posterior,  between  it  and  the  sulcus  lateralis  anterior,  the 
lateral  column,  fvniciiliis  lateralis,  ascends  from  the  spinal  cord.  After  reaching  the 
lower  end  of  the  olive,  the  column  passes  laterally  and  dorsally,  close  to  the  olive,  almost 
as  far  as  the  pons.  It  is  separated  into  a  dorsal  and  a  ventral  part  by  a  slight  furrow, 
along  which  emerge  the  delicate  root-fibres  of  the  accessory,  vagus  and  glossopharyngeal 
nerves.  The  dorsal  part  of  the  funiculus  lateralis  broadens  above  and,  in  the  region  behind 
the  tuberculum  cuneatum,  swells  into  the  tuberculum  cinereurn.  Farther  above,  it  passes 
laterally  in  company  with  the  upper  ends  of  the  column  of  GoU  and  of  Burdach.  These 
upward  and  laterally  directed  portions  of  the  column  of  Goll  and  of  Burdach  and  the 
dorsal  segment  of  the  funiculus  lateralis  collectively  constitute  the  corpus  restiforme  or 
inferior  cerebellar  peduncle,  also  called  the  crjis  cerebelli  ad  mediillani  oblongatain,  that 
passes  to  the  cerebellum.  Medially,  the  corpus  restiforme  borders  the  lateral  margin  of 
the  fourth  ventricle.  The  fossa  rhomboidea,  which  forms  the  floor  of  the  fourth  ventricle, 
overlies  the  dorsal  surface  of  the  preceding  parts. 

VENTRICULUS    OUARTUS. 

Isthmus,  metencephalon  and  myelencephalon  together  surround  the  fourth  ventricle, 
a  cavity  filled  with  a  small  amount  of  cerebro-spinal  fluid,  which  below  passes  into  the 
central  canal  of  the  spinal  cord  and  above  is  continuous  with  the  Sylvian  aqueduct. 

Three  segments  are  distinguished,  the  pars  inferior,  the  pars  intermedia  and  the 
pars  superior  ventriculi  quarti. 

The  pars  inferior  belongs  to  the  medulla  oblongata  and  is  embraced  by  the  cor- 
pora restiformia. 

The  pars  intermedia  forms  the  middle  and  broadest  portion  and  continues  above 
into  the  region  between  the  pontile  crura. 

The  pars  superior  belongs  to  the  isthmus  rhombencephali,  its  dorsal  boundary 
being  formed  by  the  brachia  conjunctiva  cerebelli  and  the  velum  medullare  anterius. 

The  floor  of  the  fourth  ventricle  is  formed  by  the  fossa  rhomboidea  and  its  roof 
by  the  anterior  medullary  velum,  the  superior  cerebellar  peduncles  or  brachia  conjunctiva, 
the  posterior  medullary  velum  and  the  tela  chorioidea.  The  posterior  medullary  velum 
and  the  tela  chorioidea  together  constitute  the  legmen  fossae  rltomboideae,  the  roof  in  the 
limited  sense.  The  edge  along  which  the  anterior  and  posterior  medullary  vela  meet  is 
known  as  the  fastigium;  at  this  place  the  fourth  ventricle  projects  into  the  medullary 
substance  of  the  cerebellum,  forming  the  tent-like  recessus  tecti.  The  pars  intermedia 
extends  laterally  on  each  side  into  the  recessus  lateralis  ventriculi  quarti.  Originally  the 
fourth  ventricle  is  a  closed  cavity,  except  above  where  it  communicates  with  the  third 
ventricle  by  means  of  the  aquaeductus  cerebri  and  below  where  it  is  continuous  with  the 
central  canal  of  the  spinal  cord.  Its  floor  and  roof  are  clothed  with  epithelium,  the  epen- 
dyma.  On  the  roof  this  epithelium  lines  the  anterior  and  posterior  medullary  vela  and 
then  continues  as  the  thin  lamina  chorioidea  epithelialis ,  which  is  attached  to  the  tela 
chorioidea  ventriculi  quarti  and  thence  is  prolonged  onto  the  borders  of  the  abutting  parts 
of  the  brain.  If  the  ventricle  be  forcibly  opened  behind  from  above,  as  when  the  tela 
chorioidea  is  removed,  the  thin  epithelial  lamina  is  likewise  torn.  The  separation  takes 
place  where  the  lamina  passed  onto  the  more  robust  surrounding  parts  of  the  brain,  only 


8o 


MORPHOLOGY. 


a  thin  white  edge,  the  taenia  ventriaili  qicarti,  remaining  along  the  borders  of  the  tear. 
The  taenia  of  the  fourth  ventricle  begins  at  the  obex,  thence  passes  onto  the  corpus  resti- 
forme,  there  forms  the  posterior  border  of  the  recessus  lateralis  and  continues  along 
the  peduncle  of  the  flocculus  and  the  posterior  medullary  velum.  The  tela  chorioidea  of  the 
fourth  ventricle  represents  that  part  of  the  pia  mater  cerebri  that  projects  between  the  ven- 
tral surface  of  the  cerebellum,  more  particularly  the  uvula  and  the  tonsilla,  and  the 
dorsal  surface  of  the  medulla  oblongata  (Fig.  84).  The  two  pial  sheets  are  united  by 
subarachnoidal  tissue.  The  tela  chorioidea  has  the  form  of  an  equilateral  triangle,  whose 
anteriorly  directed  base  is  attached  in  the  -middle  to  the  nodulus  and  at  the  sides  along 
the  posterior  medullary  velum  and  the  flocculus,  and  whose  apex  is  directed  posteriorly 
toward  the  hind  end  of  the  fourth  ventricle.  It  pushes  into  the  ventricle  villiform  proc- 
esses that  constitute  the  plexus  chorioideus  venty-iculi  quarti,  subdivided  into   medial  and 


edidlare  nnieri 
'm  g7tadrigt 


Arachnoidea 
Vehmt  medjiUare  post. 


Tela  chorioidea 


Cistenta  cerebelto-tnediillaris 
Apertura  inedialis 


Fig.  84. — Sagittal  sectic 


Medulla  oblongata 


ough  fourth  ventricle,  showing  relations  of  the  tela 
Ependyma,  red;    pia  mater,  blue. 


lateral  portions.  The  medial  plexus  consists  of  two  thin  stripes  that  pass  in  the  mid-line, 
close  together,  from  behind  forward  to  the  nodulus.  From  the  latter,  the  lateral  plexus 
continues,  on  each  side,  outward  into  the  recessus  lateralis  ventriculi  quarti.  In  the  early 
condition,  the  tela  chorioidea,  with  the  lamina  chorioidea  epithelialis,  completely  closes 
the  posterior  part  of  the  fourth  ventricle.  Later,  however,  openings  are  formed  at  those 
places,  at  which  the  tela  chorioidea  and  the  lamina  epithelialis  are  broken  through.  Such 
an  opening  is  the  apertura  tnedialis  venh'iculi  q7ia7-ti  or  the  foramen  of  Mage7idi,  situated 
in  the  posterior  part  of  the  tela  chorioidea  immediately  in  front  of  the  obex.  At  the 
sides,  in  each  lateral  recess,  is  found  the  apertura  lateralis  ventriculi  quarti  (Key-Retzii) 
or  the  fora77ie7i  of  Luschka.  Through  these  three  openings  the  ends  of  the  medial  and 
lateral  parts  of  the  choroid  plexus  of  the  fourth  ventricle  pass  and  project  into  the  sub- 
arachnoid space,  communication  between  the  ventricle  and  the  subarachnoid  space  being 
in  this  manner  established.  The  villi  which  protrude  through  the  apertura  lateralis  are 
readily  found,  since  they  lie  medial  to  the  flocculus,  between  the  latter,  the  lobulus 
biventer  and  the  tonsilla. 


FLOOR    OF   THE    FOURTH    \'ENTRICLE. 


Fossa  Rhomboidea. — The  floor  of  the  fourth  ventricle,  the  fossa  rhomboidea,  is, 
as  indicated  by  its  name,  rhomboidal  in  outline.  Its  posterior  part,  bordered  by  the  corpora 
restiformia,  belongs  to  the  myelencephalon;  its  middle  part  lies  in  the  metencephalon;  and 
its  anterior  part  belongs  to  the  isthmus.  By  means  of  a  longitudinal  furrow,  sulcus 
medianus  fossae  rhomboideae ,  it  is  divided  into  symmetrical  halves.  Transversely  coursing 
white  bands,  the  striae  medullares  or  striae  acusticae,  which  run  from  the  lateral 
recesses  toward  the  mid-line,  separate  the  pars  superior  from  the  pars  inferior 
fossae  rhomboideae.  The  part  of  the  fossa  included  between  the  medullary  striae  constitutes 
the    pars   intermedia. 

The  striae  medullares  present  many  variations  in  their  course  and  develop- 
ment.      They    may    be    wanting    or    many,    but    are    seldom     identical    in    development 


Fossa  mediana 


Area  acustid 


Trigoni 

m  N  XI I 

Corpus  r 

esll/crme 

FunUul. 

separans 

Area 

Postrenta 

Clava 

Tubtrci 

I.  cvneat. 

Tuberc. 

cinereunt 

Obex 

rmed.  post. 
r.  gracilis     Fiiti.  ciineat.      Fun.   lateralis  Sulc.  lateral,  post. 

Vn„  8s.— Dorsal  surface  of  the  medulla  oblongata.     Fossa  rhomboidea. 


and  course  on  the  two    sides.      Often    they    run    obliquely  outward  and  upward  from  the 
sulcus  medianus. 

The  pars  inferior  of  the  ventricle  deepens  in  its  lower  portion,  presents  several  fields 
definecJ  by  furrows  and,  on  account  of  its  peculiar  shape,  is  called  the  calamus  scriptorius. 
At  the  lower  border  of  the  pars  inferior  lies  the  obex,  a  thin  white  medullary  sheet  from 
which  the  taeniae  ventriculi  quarti  pass  laterally.  Immediately  in  front  of  the  obex,  where 
the  sulcus  medianus  sinks  into  the  central  canal  of  the  spinal  cord,  is  a  small  depression,  the 
venlriculus  Arantii.  In  the  pars  superior,  the  median  sulcus  widens  into  the  fossa 
mediana.  On  each  side  of  the  median  furrow,  a  flat  ridge,  the  emincntia  medialis,  extends 
the  entire  length  of  the  ventricular  floor.  This  ridge  is  narrow  in  its  lower  part  and  forms 
6 


82  MORPHOLOGY. 

a  triangular  field,  the  trigonum  nervi  kypoglossi,  whose  base  is  above  at  the  striae  medul- 
lares  and  apex  below,  directed  toward  the  ventriculus  Arantii. 

On  careful  inspection,  two  special  divisions  of  this  field  are  ^recognized,  an  outer 
broader  part,  the  area  plumifor7nis  (Retzius),  and  an  inner  narrower  one,  the  area 
medialis  trigoni  nervi  kypoglossi  (Retzius).  At  the  border  between  those  two  fields 
are  to  be  seen  mostly  short,  obliquely  coursing  delicate  furrows  and  folds,  and  likewise 
a  thin  feathery  band.  Such  markings  are  often  visible  also  at  the  lateral  border  of  the 
trigonum  hypoglossi.  Retzius,  therefore,  named  this  lateral  and  broader  field,  ' '  area 
plumiformis. ' ' 

In  the  upper  part  of  the  ventricular  floor,  the  eminentia  medialis  is  broader  and  pro- 
jects more  into  the  ventricle.  The  elevation  is  termed  the  colliculiis  facialis.  Laterally,  the 
eminentia  medialis  is  defined  by  the  sulcus  limiiatis,  which  in  the  pars  superior  widens  into 
the  fovea  superior,  and  in  the  pars  inferior  into  the  fovea  inferior.  Below  the  fovea 
inferior,  and  lateral  to  the  trigonum  hypoglossi,  is  seen  a  gray  oblique  triangular  field, 
known  as  the  ala  cinerea,  which  begins  pointed  at  the  fovea  inferior  and  broadens  toward 
the  lower  border  of   the  fossa  rhomboidea. 

In  front  of  the  posterior  border  of  the  fossa  and  behind  the  ala  cinerea,  lies  a 
small  gray  mammillated  field,  the  area  postrema,  that  extends  from  the  mid-line  along  the 
lower  border  of  the  ventricle  forward  and  outward.  A  light  narrow  band,  known  as  the 
ftmicuhis  separans,  runs  from  the  opening  central  canal  outward  and  forward,  between 
the  area  postrema  and  the  ala  cinerea. 

The  fovea  superior  is  accompanied  laterally  by  a  bluish  colored  area,  the  locus  caeru- 
leus.  The  latter  and  the  superior  fovea  exhibit  small  furrows  and  folds,  rugae  loci 
caerulei  et  foveae  stiperioris,  which  may  often  be  followed,  for  a  considerable  distance,  for- 
ward toward  the  isthmus  and  backward  toward  the  recessus  lateralis.  To  the  outer  side 
of  the  sulcus  limitans,  lateral  to  the  fovea  superior,  the  fovea  inferior  and  the  ala  cinerea, 
the  area  acustica,  is  seen  as  a  flat  elevation,  which  toward  the  recessus  lateralis  presents 
the  tuberculuvi  acusiicum.  The  funiculus  separans,  above  noted,  courses  toward  the 
lower  inner  end  of  the  area  acustica  and  there  disappears. 


THE  GRAY  MASSES  OF  THE  RHOMBENCEPHALON. 

In  the  floor  of  the  trigoyium  leninisci,   in  the  isthmus,  lies  the  nucleus  letmiisci. 

The  pons  includes  a  larger  ventral  portion,  the  pars  basilaris  poniis,  and  a  smaller 
dorsal  one,  the  pa?-s  dorsalis  pontis.  These  two  divisions  are  readily  seen  in  a  cross- 
section.  The  basal  part  exhibits  numerous  transversely  coursing  white  fibre-strands  that 
continue  laterally  into  the  pontile  crura  or  middle  cerebellar  peduncles.  In  the  lower 
part  of  the  basilar  division,  between  the  thin  white  fibre-bundles,  grayish  lamellfe  repre- 
sent the  cross-sections  of  the  tracts  of  fibres,  which  descend  from  the  cerebral  peduncles, 
pass  through  the  entire  pons  and  continue  to  the  medulla  oblongata  and  the  spinal  cord. 
These  are  the  pyramidal  tracts,  the  fasciculi  longitudinales  pyramidales.  The  fibrae 
pontis  superficiales  are  seen  as  transversely  coursing  fibres  that  pass  ventral  to  the  pyram- 
idal tracts,  while  the  fib^'ae  pontis  profundae  run  dorsal  to  or  partly  through  the 
pyramidal  strands.  The  pontile  nuclei,  7mclei  pontis,  are  small  masses  of  gray  substance 
lying  scattered  between  the  bundles  of  fibres. 


NUCLEI    OF  THE    HIND-BRAIN. 


83 


The    pars    dorsalis    pontis,    also    termed   the  tegmentum  pontis,    appears   gray   in 
transverse  sections.      It  contains  the  following  nuclei  : — 

The  nucleus  ner\i  abducentis,  within  the  coUiculus  facialis, 

The  nucleus  ner\i  facialis, 

The  nucleus  motorius  et  sensibilis  nervi  trigemini, 

The  nucleus  tractus  spinalis  nervi  trigemini, 

The  nuclei  nervi  acustici,   within  the  area  acustica,   embracing  : — 

Nucleus  medialis 

Nucleus   dorsalis 

Nucleus  medialis 

Nucleus  lateralis  (Deiters) 

Nucleus  superior  (Bechterew) 

Nucleus  n.   vestibularis  spinalis 
The  nucleus  olivaris  superior, 
The  nucleus  corporis  trapezoidei. 
The  nuclei  reticulares  tegmenti. 


nervi  cochleae. 


nervi  vestibuli, 


■Within  the  cerebellum  (Fig.    87),  in  addition  to  the  corte.x  or  substantia  corti- 
calis    covering  the    entire    surface,    special    gray    masses    are    found    within    the    corpus 


f-      -    //      l-,ntr!cU. 


Irgmfntlim  foi.  tis 


N.   trigeminus 


Motor  and  sensory 
trigemii 


..Pyrnmidiil  tracts 
'itrntnm  siiferficialg  pontis 


Pig.  86. — Cross-section  of  brain-stem  in  region  of  pons. 


medullare.  In  the  medial  [lart  of  the  hemisphere  lies  the  hhcIchs  denlatiis, 
which  appears  as  a  much  plicated  lamella  of  gray  substance  with  a  medially  directed 
opening,  the  kilus  nuclei  dcntati.  Within  the  worm,  the  roof -nucleus ,  nucleus  fastigii 
or  nucleus  tecti,  lies  on  each  side  of  the  mid-line.  Between  the  nucleus  fastigii  and  the 
nucleus  dentatus,  two  additional  centres  are  found,  the  7iuclci  globosi,  small  gray 
masses  lateral  to  the  roof-nucleus,  and  the  nucleus  embolijormis,  medial  to  the 
dentate  nucleus. 


MORPHOLOGY, 


Niiclens  Jasiigii 


Within  the  medulla  oblongata,  in  the  fasciculus  gracilis  within  the  clava,  lies 
the  nucleus  fasciculi  gracilis,  while  in  the  fasciculus  cuneatus,  in  its  position  correspond- 
ing to  the  tuberculum  cuneatum, 
lies  the  nucleus  fasciculi  cuneati. 
The  tuberculum  cinereum  corre- 
sponds to  the  nucleus  tractus  spi- 
nalis Jiervi  trigeniini.  Within  the 
olive  are  found  the  fiucletis  oliva- 
ris  inferior,  with  the  nuclei  of  the 
two  accessory  olives,  the  nucleus 
olivaris  accessorius  ventralis  and 
dorsalis.  The  nuclei  arcicati  lie 
ventral  to  the  pyramidal  tracts, 
while  within  the  lateral  columns 
are   the   mcclei  laferales. 


Fig.  88. — Diagram  of   the  brain-stem,  dorsal   aspect,  showing   the  locatic 
nuclei  are  red,  sensory  nuclei  a 


uclei  of  the  cerebral 


The  floor  of  the  trigonum  hypoglossi  contains  the  nucleus  nervi  hypoglossi.      Close 
to  the  latter  but  within  the  floor  of  the  ala  cinerea,   is  the  sensory  7iucleus  of  the  vagus 


SUMMARY    OF    RHOMBENCEPHALON. 


85 


nerve,  which  anteriorly  is  continuous  with  the  like  nucleus  of  the  glossopharyngeal  nerve. 
In  this  region,  medial  to  the  ala  cinerea,  the  motor  nucleus  dorsalis  of  the  glossopharyn- 
geal and  vagus  nerves  appears  as  a  small  group  of  cells.  The  nucleus  tractus  solitarii 
occupies  the  elongation  of  the  sensory  nucleus  of  the  glossopharyngeal  and  vagus  nerves. 
Somewhat  lateral,  but  more  deeply  placed,  lies  the  nucleus  ventralis  or  nucleus  ambiguus 
of  the  ninth  and  tenth  nerves.      The  caudal  prolongation  of  the  nucleus   ambiguus  con- 


FlG.  89. — Diagra 


of   brain-stem,  lateral   aspect,  showing  locatit 
sensory  nuclei  a 


of   nuclei   of   cerebral 


tains  the  elongated  nucleus  tiervi  accessorii,  whose  spinal  part  reaches  into  the  ventral 
horn  of  the  spinal  cord.  The  nerve-cells  within  Xhe  formatio  reticularis,  occurring  scattered 
or  in  small  groups,   constitute  the  nucleus  of  the  formatio  reticularis. 

The  more  important  of  these  nuclei  are  discussed  at  greater  length  in  connection 
with  the  Fibre-Tracts.  The  positions  of  the  nuclei  of  the  cerebral  nerves  are  diagram- 
matically  shown  in  Figs.   88  and  89. 

SUMMARY    OF   THE    RHOMBENCEPHALON. 
To  the  rhombencephalon  or  hind-brain  belong : 

The  isthmus  rhombencephali, 
The  metencephalon, 
The  myelencephalon. 
It  encloses  the  fourth  ventricle. 


To  the  isthmus  rhombencephali  belong  : 

Dorsal — The  brachia  conjunctiva  cerebt: 
The  velum  meduUare  anterius, 
The  trigonum  lemnisci  ; 
Ventral — The  crura  cerebri. 

To  the  metencephalon  belong  : 

The  pons  and  the  cerebellum. 


86  MORPHOLOGY. 

The  cerebellum  is  subdivided  into  the  worm  arid  the  hemispheres.  More  or  less 
deeply  penetrating  fissures  separate  the  lobes  of  the  hemispheres  from  one  another.  The 
chief  segments  are  the  lobus  superior,  the  lobus  posterior  and  the  lobus  inferior,  each  of 
which  is  made  up  of  lobules.  The  individual  lobes  and  lobules  of  the  hemispheres  corre- 
spond to  definite  divisions  of   the  worm. 

The  myelencephalon,  or  the  medulla  oblongata,  has  as  its  upper  boundary, 
ventrally  the  lower  border  of  the  pons,  dorsally  the  striae  medullares  fossae  rhomboideae. 
Below,  the  medulla  passes  into  the  spinal  cord,  its  ventral  boundary  being  the  lower  end 
of  the  pyramidal  decussation.  Dorsal,  behind  the  rhomboid  fossa,  are  the  dorsal  and 
lateral  columns,  with  their  tubercula,  and  the  restiform  bodies.  Ventral,  lie  the  pyramids 
and  the  olives. 

The  fourth  ventricle  has  as  its  roof  the  velum  medullare  anterius,  the  brachia 
conjunctiva  cerebelli,  the  velum  medullare  posterius  and  the  tela  chorioidea  ;  as  its  floor, 
the  fossa  rhomboidea.  It  is  connected  with  the  third  ventricle  by  means  of  the  aquae- 
ductus  cerebri,  below  is  continuous  with  the  central  canal  of  the  spinal  cord,  and  com- 
municates with  the  subarachnoid  space  by  means  of  the  apertura  mediana  (foramen 
Magendii)  and  the  aperturae  laterales   (foramina  Luschkae). 

The  most  important  masses  of  gray  substance  within  the  rhombencephalon  are  : 

The  nucleus  lemnisci. 

The  nucleus  pontis. 

The  substantia  corticalis  cerebelli, 

The  nucleus  dentatus 

The  nucleus  fastigii 

The  nucleus  globosi     , 

The  nucleus  emboliformis 

The  nucleus  gracilis. 

The  nucleus  cuneatus. 

The  nucleus  lateralis. 

The  nucleus  arcuatus. 

The  nucleus  olivaris  inferioris, 

The  nuclei  nervorum,   within  the  floor  of  the  fourth  ventricle. 


THE  MENINGES. 

The  membranes  investing  the  brain  are  three  :  the  dura  mater,  the  arachnoid  and 
the  pia  mater. 

The  dura  mater  forms  the  outermost  covering  of  the  brain.  Beneath  it  lies  the 
arachnoid,  a  delicate  transparent  membrane  that  is  separated  from  the  dura  by  the  sub- 
dural space.  The  innermost  covering  is  the  pia  mater,  separated  from  the  arachnoid  by 
the  subarachnoidal  space.  The  arachnoid  and  the  pia  have  been  also  regarded  as  the 
outer  and  inner  layers  of  the  soft-brain  membrane,  the  leptomeni?ix ,  in  contrast  to  the 
hard  brain-membrane,   the  pachymeninx,   represented  by  the  dura. 


cerebelli. 


BRAIN-MEMBRANES. 


87 


DURA    MATER. 

The  dura  mater  consists  of  two  lamella-.  The  outer  lamella,  which  lies  against  the 
bone  and  serves  as  the  inner  periosteum  of  the  cranial  case,  consists  of  soft,  loose  vascular 
connective  tissue.  The  inner  lamella  is  denser,  made  up  of  fibrous  connective  tissue,  and 
contains  few  blood-vessels.  While  the  outer  layer  appears  as  periosteum  and  is  prolonged 
on  the  cerebral  nerves  as  robust  sheaths,  the  inner  layer  comes  into  closer  relation  with  the 
brain,  since  it  sends  processes  between  the  larger  divisions  of  the  brain.      Such  processes  are  : 

I.  The  falx  cerebri,  or  falx  cerebri  major,  which,  penetrating  between  the  hemi- 
spheres, begins  in  front  at  the  crista  galli,  attached  by  its  convex  upper  border  to  the 
sides  of  the  sulcus  sagittalis  of  the  cranial  \ault,  and  extends  backward  as  far  as  the 
protuberantia  occipitalis  interna.  Between  the  outer  and  inner  lamellae,  along  the  upper 
convex  border  of  the  falx,  is  a  blood-space,  which  is  triangular  in  cross-section  and  known  as 
the  sinus  sagittalis  superior.  The  lower  concave  border  of  the  sickle-like  falx  is  free  and 
encloses  the  smaller   sifius  sagittalis    inferior.       From  the  internal  occipital  protuberance 

Sinus  sagittalis  sitperior     Grannlatioms  Pactitioni 


Craniitm 

Spatiiim  epidural. 

Dura  mater 

Sfiatium  stihdural. 

Arachnoidea 

Sfintiiim  sitharach. 

Pia  mater 


Substantia  corticatis  cereb, 


Fig.  90. — Schematic  section  through  the  skull  and  the  meninges. 


forward,  the  falx  is  attached  to  the  tent-like  tentorium  cerebelli,  the  line  of  junction  being  the 
tent-edge,  while  the  border  attached  to  the  crista  galli  is  the  crest-edge.  In  front,  the  falx 
only  incompletely  separates  the  two  frontal  lobes,  but  behind  its  height  is  so  increased, 
that  it   penetrates  almost,   but    not    quite,   to  the    upper    surface    of  the  corpus  callosum. 

2.  The  falx  cerebelli,  or  falx  cerebri  minor,  which  forms  a  small  sagittal  pro- 
longation of  the  large  falx,  penetrates  between  the  cerebellar  hemispheres  and  descends 
from  the  internal  occipital  protuberance  to  the  foramen  magnum.  The  convex  border 
encloses  the  sinus  occipitalis  and  is  attached  along  the  crista  occipitalis.  Corresponding 
to  the  terminal  limits  of  the  crest,  the  cerebellar  falx  divides  into  two  diverging  arms, 
which  enclose  the  continuations  of   the  sinus  occipitalis. 

3.  The  tentorium  '  cerebelli,  which  forms  a  dorsally  arched  transverse  partition 
between  the  basal  surface  of  the  occipital  lobes  of  the  cerebrum  and  the  dorsal  surface  of 
the  cerebellum.  The  outer  convex  margin  is  attached,  on  each  side,  along  the  lineae 
transversae  of  the  occipital  and  parietal  bones,  where  it  encloses  the  sinus  transversus, 
and  along  the  dorsal  edge  of  the  petrous  portion  of  the  temporal  bone,  where  it  conveys 
the  sinus  pelrosus  superior.     Thence  the  attachment  of  the  tentorium    [xisses  to  the  pro- 


88  '  MORPHOLOGY. 

cessus  clinoides  anterior.  In  front,  the  free  inner  margin  of  the  tentorium  meets  the  outer 
one  and  then  extends  backward  and  sHghtly  upward  to  unite  with  the  lower  edge  of  the 
falx  cerebri.  Along  this  line  of  union  lies  the  si7uis  rectus,  which  in  front  receives  the 
vena  cerebri  inagyia  Galeni  (Fig.  55)  and  behind  opens  into  ihe  conflice/is  sinuum  or  the 
torcular   Herophili. 

4.  The  diaphragma  sellae  turcicae,  which  forms  a  bridge  of  diiral  tissue  over 
this  depression  in  the  sphenoid  bone.  Between  the  basal  and  dorsal  lamellee  of  the 
diaphragma  sellae  turcicae  lies  the  hypophysis  or  pituitary  body.  An  opening  in  the  middle 
of   the  membrane,   the  foramen  diapkragtnatis,   affords  passage  to  the  infundibulum. 

ARACHNOIDEA. 

This  delicate  transparent  membrane  consists  of  connective  tissue  and  is  devoid  of 
blood-vessels.  It  is  separated  from  the  dura  by  the  subdural  space  and  connected  with 
the  pia  by  strands  of  connective  tissue.  These  strands  form  the  subarachnoidal  tissue, 
and  the  cleft  between  the  arachnoid  and  the  pia  is  the  subarachnoidal  space.  The  latter 
is  traversed  by  the  connective  tissue  trabeculee  and  plates  of  the  subarachnoidal  tissue 
and  contains  a  fluid,  the  liquor  cerebro-spinalis,  in  considerable  quantity.  The  subarach- 
noidal space  communicates  with  the  ventricles  by  means  of  the  foramen  Magendii  and 
the  foramina  Luschkae  (page  80).  Over  the  cerebral  convolutions  the  subarachnoidal 
tissue  is  scanty,  in  these  localities  the  arachnoid  and  the  pia  being  fused  into  a  common 
membrane.  Over  the  cerebral  fissures,  on  the  contrary,  the  space  between  the  two 
membranes  is  larger,  since  the  pia  penetrates  into  the  fissures.  The  large  spaces  are 
found  principally  at  the  base  of  the  brain  and  where  the  latter  passes  into  the  spinal 
cord  ;  in  these  locations,  at  certain  places,  the  arachnoid  is  widely  separated  from  the  pia, 
resulting  in  the  formation  of  the  cistemae  subarachnoideales.      Such  spaces  are  : 

The  cisterna  cerebello-medullaris,  between  the  posterior  border  of  the  cerebellum  and 
the  medulla  oblongata  ; 

The  cisterna  fossae  Sylvii,   over  the  Sylvian  fossa  ; 

The  cisterna  chiasmatis,   surrounding  the  optic  chiasm  ; 

The  cisterna  interpeduncularis ,   between  the  cerebral   crura  ; 

The  cisterna  aynbiens,  ascending  laterally  from  the  cerebral  peduncles  to  the  corpora 
quadrigemina  ; 

The  cisterna  cojporis  callosi,   along  the  convex  dorsal  surface  of  the  callosum. 

In  certain  places,  as  on  both  sides  of  the  sinus  sagittalis  superior  or  along  the  sinus 
transversus,  villous  projections  from  the  outer  surface  of  the  arachnoid  push  before  them 
the  thin  dura  mater  and  encroach  on  the  venous  sinuses.  Such  elevations  are  called  the 
arachtioidal  villi  or  Pacchonian  gratiulations  (Fig.  90).  According  to  the  investigations  of 
Key  and  Retzius,  these  structures  facilitate  the  passage  of  serous  fluid  into  the  venous  spaces. 

PIA  MATER. 
The  innermost  brain-membrane  consists  of  delicate  bundles  of  connective  tissue,  con- 
tains numerous  blood-vessels,  and  directly  invests  the  surface  of  the  brain,  penetrating  to 
the  bottom  of  all  the  fissures.  By  means  of  the  subarachnoidal  tissue,  the  pia  is  attached 
to  the  arachnoid.  Between  the  pia  and  the  surface  of  the  brain,  there  exists  only  a  very 
narrow  cleft,   the  subpial  or  epicerebral  space. 


THE    SPINAL    CORD. 


89 


THE  SPINAL  CORD. 


The  spinal  cord  or  medulla  spinalis  presents  a  compressed  cylindrical  column,  some- 
what more  flattened  in  front  than  behind,  that  is  enclosed  within  its  protecting  membranes 
and  only  incompletely  fills  the  vertebral  canal.  Above,  it 
passes  into  the  medulla  oblongata,  the  upper  limit  corre- 
sponding to  the  lower  end  of  the  pyramidal  decussation. 
Below,  the  spinal  cord  reaches  to  the  level  of  the  first 
or  second  lumbar  vertebra.  It  is  not  everywhere  of  : 
equal  thickness,  but  in  two  places  exhibits  spindle-shaped 
enlargements  (Fig.   91)  : 

a.  In  the  cervical  region  of  the  spine  the  cervical 
enlargement,  intiunescentia  cervicalis,  from  the  third  cervical 
to  the  second  thoracic  vertebra  ; 

b.  In  the  lower  part  of  the  thoracic  spine  the  lumbar 
enlargement,  intumesce7itia  lumbalis,  from  the  ninth  thoracic 
to  the  second  lumbar  \-ertebra. 

Both  enlargements  correspond  to  the  regions  in  which 
the  large  limb-nerves  arise. 

The  lumbar  enlargement  below  passes  over  into  a 
short  conical  segment,  the  C07ius  mediillaris  or  co7ius 
terminalis,  from  which  proceeds  a  long  delicate  thread-like 
process,  the  filutn  terminale. 

The  average  length  of  the  spinal  cord  is  45  cm.  in 
men,  and  from  41-42  cm.  in  women.  In  accordance  with 
the  pairs  of  spinal  nerves  given  off  from  the  cord,  we  recog- 
nize a.  pars  cervicalis,  from  which  the  cervical  nerves  emerge  ;  a  pars  thoracalis,  from  which 
the  thoracic  nerves  arise,  and  a  pars  lumbalis,  from  which  the  lumbar  and  the  sacral  nerves 
are  derived. 

EXTERNAL   CONFIGURATION. 

The  anterior  or  ventral  surface  of  the  spinal  cord  is  cleft  in  the  mid-line  by  a  deep 
longitudinal  furrow,  \.\\^Jissura  mcdiana  anterior ;  the  posterior  or  dorsal  surface  is  modelled 

by  a   superficial    longitu- 

iermedius  posterior  ^inal    grOOVe,     the     SlllcUS 

mcdianus  posterior.  By 
means  of  these  two  fur- 
rows the  spinal  cord  is 
divided  into  symmetrical 
halves.  Lateral  to  the 
posterior  median  sulcus, 
in  each  half  runs  the 
sulcus  lateralis  posterior, 
along  which  the  pos- 
terior root-bundles  enter. 


Filu 

termit 

Front 

view    of    the  s 

ord. 

Schematic. 

FuHuulus  post fr hi 

Radix  po$ttrior 


Sulc.  tned. 
Fasciculus  gracilis        post.        Sulcus 
Fasc.  cuneaius       ^ 


Funiculus  lateral. 


Radix  anterior 


.-'  Sulcus  lateralis  poster. 
Cornu  posierins 
Forntatio  rettculart 
Colnmna  lateralis 


Cornu  anterius 

Sulc.  lat.  anterior 


THcdiana  anterior 


FunieuliiM  anterior 
Pig,  92. — Transverse  section  of  the  spinal  cord. 


go 


MORPHOLOGY. 


93. — Schematic 


Radix  ant, 

representation    of    the 


formation  of   the   spinal 


Lateral  to  the  anterior  median  fissure,  on  each  side  extends  the  stdcus  lateralis 
ante7-ior,  which  is  not  a  continuous  furrow,  unless  the  emerging  anterior  root-fibres  are 
torn  away.  In  the  upper  thoracic  and  the  cervical  region,  an  additional  delicate  longi- 
tudinal groo\'e,  the  sulcus  intermedius  posterioi',  is  distinguishable  between  the  median 
and  lateral  posterior  sulci.      The  anterior  root-fibres  that  emerge  along  the  anterior  lateral 

sulcus  form  individual  bundles, 
the  radices  anteriores,  sepa- 
rated from  one  another  by- 
intervals.  The  posterior  root- 
fibres,  which  enter  along  the 
posterior  lateral  sulcus  in  an 
unbroken  row,  likewise  form 
outwardly  converging  bundles, 
the  radices  postei-iores.  Each 
pair  of  anterior  and  posterior 
root-bundles  passes  to  a  defi- 
nite foramen  intervertebrale 
(Fig.  93).  Here,  the  posterior 
root  presents  a  small  fusiform  swelling,  the  ganglion  spinale,  and  then  unites  in  its  fur- 
ther course  with  the  corresponding  anterior  root,  thereby  forming  the  spinal  nerve, 
which    latter    divides    into    an    anterior    and    posterior    division. 

The  emerging  root-bundles  run  not  only  outward,  but  at  the  same  time  caudalward, 
and,  indeed,  the  more  so  the  nearer  to  the  caudal  end  of  the  spinal  cord  they  emerge. 
In  the  lumbar  region,  the  course  of  the  nerve-roots  within  the  vertebral  canal  is  nearly 
parallel  with  the  long  axis  of  the  cord,  so  that  the  conus  medullaris  and  the  filum 
terminale  lie  in  the  midst  of  a  generous  bundle  of  nerve-roots,  which,  on  account  of  the 
supposed  resemblance  to  a  horse's  tail,   is  designated  the  cauda  equina. 

By  means  of  the  longitudinal  furrows,  the  spinal  cord  is  subdivided  into  the  following 
columns  : 

The  funiculus  anterior,  between  the  anterior  median  fissure  and  the  anterior  lateral 
sulcus  ; 

The  funiculus  lateralis,  between  the  anterior  and  posterior  lateral  sulci  ; 
The  fu7iiculus  posterior,  between  the  posterior  median  fissure  and  the  posterior 
lateral  sulcus.  The  posterior  column  is  separated  by  the  sulcus  intermedius  posterior 
into  a  medial  and  a  lateral  division,  the  medial  one  being  known  as  the  fasciculus 
gracilis,  or  Goll' s  column,  and  the  lateral  one  as  the  fasciculus  ciuieatus,  or  BurdacK s 
column. 

INTERNAL    CONFIGURATION. 

Even  with  the  unaided  eye,  one  can  readily  distinguish  gray  and  white  substance 
in  a  transverse  section  of  the  spinal  cord.  When  cut  across,  the  centrally  situated  gray 
substance  appears  H-form  in  outline.  The  bridge  of  gray  substance  connecting  the  two 
limbs  of  the  H,  encloses  the  central  canal,  canalis  centralis,  which  is  immediately  sur- 
rounded by  the  substantia  gelatinosa  centralis  and  lined  with  ependyma.  Above,  the 
central  canal  widens  at  the  transition    of   the   spinal  cord  into  the  medulla  oblongata  and 


THE   SPINAL    CORD. 


91 


passes  over  into  the  fourth  ventricle.  Below,  at  the  lower  end  of  the  conus  terminalis, 
it  expands  into  the  vejitriadus  terminalis  (Krause),  becomes  again  narrow  at  the 
transition    into    the   filum  terminale  and,   finally,   ends  blindly. 

The  part  of  the  gray  bridge  that  passes  behind  the  central  canal  is  known  as  the 
commissura  posterior,  that  which  lies  in  front  is  the  conimissiira  grisea  anterior.  In 
front  of  the  latter,  between  it  and  the  bottom  of  the  anterior  median  fissure,  is  the 
coTntnissura  alba  anterior. 

The  gray  substance,  in  each  half  of  the  spinal  cord,  presents  in  front  a  thick 
swelling,  the  anterior  horn  or  cornu  antcrius,  and  behind  a  more  slender  part,  the  poste- 
rior horn  or  cornn  posterius.  Since  the  gray  substance  extends  continuously  throughout 
the  entire  length  of  the  cord,  the  anterior  and  posterior  horns  appear  in  longitudinal 
sections  as  columns  :    they  are    called  also,   therefore,   the    columnae   irriscac.      The  lateral 


Mnygiiinl  zo. 


Subst.  g>;lntirwsa  Rotandi 
Captit  0/  posterior  horn 


Formaiio  reticular 


Clarke's  coluii 


Co)ltwtsttira  alba  Anterior  root 

Fig,  94. — Transverse  section  of  the  spinal  cord. 


part  of  the  gray  substance,  in  the  lower  cervical  and  the  upper  thoracic  regions  of  the 
cord,  becomes  more  independent  and  there  forms  the  lateral  horn  or  columna  lateralis. 
In  the  entire  cervical  and  upper  thoracic  cord,  the  gray  substance  extends  into  the  white 
matter  as  a  network  of  gray  trabeculae  and  strands,  which  occupy  the  angle  between 
the  lateral  and  posterior  horns  and  constitute  the  formatio  reticularis.  The  posterior 
cornu  begins  ventrally  as  the  base,  then  becomes  narrower  and  forms  the  neck,  cervix 
columnae  posterioris ;  dorsally  follow  the  head  of  the  horn,  caput  colnmnae-,  and  the 
point,  apex  columnae  posterioris,  which  latter  embraces  a  crescentic  field,  the  substantia 
gelatinosa  Rolandi,  and  the  dorsally  situated  marginal  zone.  Medial  to  the  neck  of  the 
posterior  cornu  and  close  to  the  posterior  commissure,  one  finds  the  nucleus  dorsalis  or 
Clarke' s  column  as  a  small  group  of  cells  within  the  gray  substance  of  the  upper 
lumbar,   the  entire  thoracic  and  the  lower  cervical  regions. 

The  white  substance  surrounds  the  gray  and  is  subdivided,  as  already  noted, 
into  three  tracts — the  anterior  column,  between  the  anterior  median  fissure  and  the  anterior 
roots,  the  posterior  column,  between    the  posterior  median  fissure  and  the  posterior  roots, 


92 


MORPHOLOGY. 


and  the  lateral  column,  between  the  anterior  and  posterior  roots.  The  posterior  column 
is  further  divided  by  the  sulcus  intermedius  posterior  into  the  medially  situated  fasciculus 
gracilis  or  GoU's  column,  and  the  laterally  placed  fasciculus  cuneatus  or  Burdach's 
column. 

In  the  essentials,  the  make-up  of  the  spinal  cord  is  the  same  in  its  various 
segments,  the  central  gray  substance  in  the  characteristic  H  being  everywhere  enclosed 
by  the  white  matter.  The  size  and  form  of  the  cord  in  cross-sections,  as  well  as  the 
proportions  of  the  gray  and  white  substance,  however,  vary  in  the  individual  regions. 
In  regard  to  size,  the  stronger  development  in  the  cervical  and  lumbar  enlargements  is 
at  once  noticeable.  So  far  as  the  form  is  concerned,  transverse  sections  are  so  charac- 
teristic in  the  different  regions  that,  within  certain  hmits,  the  region  from  which  a  section 
has  been  taken  can  be  determined  from  such  data  alone.  Thus,  cross-sections  of  the 
cord  in  the  cervical  region,   particularly  at    the  level  of  the    IV-VIII    nerve,    and  in  part 


T/IJE 


Li 


Fig.  95. — Transverse  sections  of  the  s^jinal  cord  at  difEerent 


'ical;   Th,  thoracic;  Z,,  lumbar;  5.  sacral. 


also  in  the  highest  thoracic  segments  are  transversely  oval ;  in  the  thoracic  region  the 
cross-section  is  almost  circular  ;  while  in  the  lumbar  region  it  is  more  quadrate,  with 
more  marked  ventral  flattening.  The  quadrate  form  is  especially  evident  in  the  sacral 
and  likewise  in  the  coccygeal  cord,  where,  however,  in  contrast  to  the  lumbar  region, 
the  strongest  flattening  is  dorsal  with  coincident  ventral  narrowing. 

Regarding  the  proportion  of  the  gray  and  the  white  substance,  it  is  readily  seen 
that  the  gray  substance  is  most  abundant  in  those  segments  from  which  the  large  limb- 
nerves  arise,  that  is  in  the  cervical  and  lumbar  enlargements.  In  these  segments  the 
great  development  of  the  anterior  horns  is  particularly  evident.  The  gray  substance  in 
the  dorsal  cord,  on  the  contrary,  is  poorly  developed,  the  H-form  being  here  seen  to 
best  advantage.  The  white  substance  exhibits  a  robust  development  in  the  cervical,  as 
well  as  the  thoracic  region.  Towards  the  lumbar  cord  it  progressively  decreases  in 
amount  and,  in  the  sacral  region  and  toward  the  conus  medullaris,  the  white  matter  forms 
only  a  thin  peripheral  zone  surrounding  the  gray  matter,  which  at  these  levels  con- 
siderably exceeds  in  amount  the  white. 


SPINAL   MENINGES. 


93 


THE    MEMBRANES    OF   THE    SPINAL    CORD. 

As  is  the  brain,  so  also  the  spinal  cord  is  surrounded  by  three  envelopes — the 
dura  mater,   the  arachnoid  and  the  pia  mater. 

Dura  mater  spinalis.  This  membrane  forms  a  strong  fibrous  investment  consist- 
ing of  two  layers,  the  outer,  which  fuses  with  the  periosteum  of  the  vertebrae,  and  an 
inner,  which  is  the  spinal  dura  proper.  The  space  between  these  two  layers  is  filled 
with  loose  connective  tissue,  contains  the  large  venous  plexus  and  is  traversed  by  lymph- 
spaces  ;    it  is  the  cavum  intcrduralc  or  cavum  epidurale.      The    dura    extends  as  a    long 


Fig.  96. — Schen 


representation   showing   relations  of   the  spinal  meninges  to  one  another  ; 
Dura  is  yellow;  arachnoid,  green;  pia.  with  ligamentum  denticulatum,  1 


wide  sac  over  the  conus  medullaris,  narrows  at  the  level  of  the  second  or  third  sacral 
vertebrae,  thence,  as  the  filum  durac  ?natns  sphialis,  clothes  the  filum  terminals  and 
finally  passes  into  the  periosteum  of    the  coccyx. 

Arachnoidea  spinalis.  This  is  a  delicate  vascularless  membrane,  separated  from 
the  dura  mater  by  the  cavum  subdurale  and  from  the  pia  mater  by  the  cavum  sxibarachnoi- 
deale.  It  is  connected  with  the  subarachnoidal  fibres, .  which  are  particulary  robust  and 
numerous  toward  the  sulcus  medianus  posterior  ;  in  the  lower  cervical  and  in  the  thoracic 
regifin,  they  form  a  special  partition,  the  septum  subarachnoideale  or  septum  cevicale 
intermcdum.      Within  the  subarachnoidal  space  the  liquor  cerebro-spinalis  circulates. 

Pia  mater  spinalis.  This  membrane  encloses  the  spinal  cord  as  a  delicate  vas- 
cular envelope  and  forms,  by  penetrating  within  the  anterior  median  fissure,  the  septum 
antcrius.  The  pia  is  connected  with  the  dura  mater  by  means  of  the  ligamentum  dentic- 
ulatum.  The  latter  consists  of  from  19—23  small  triangular  processes,  with  their  bases 
attached  to  the  pia,  which  extend  outward  from  the  lateral  surface  of  the  cord  between 
the  anterior  and  posterior  roots  of  the  spinal  nerves,  to  be  attached  by  their  ])oints  to 
the  dura  mater.  The  ligamentum  denticulatum  serves  as  a  suspensory  band  that  holds 
the  spinal  cord   in  [)<)sition. 


PART  II. 
THE   FIBRE-TRACTS. 


THE  FIBRE-TRACTS. 


METHODS    OF    STUDYING   THE   FIBRE-TRACTS. 

The  older  anatomists  contented  themselves  with  the  task  of  describing  the  brain 
simply  from  the  exterior  and,  in  a  sense,  without  further  leading  conceptions.  In  this 
period  originated  the  terminolog)-  that  owes  its  existence  to  merely  purely  superficial  and 
accidental  resemblances.  As  examples,  one  recalls  the  designation  of  the  corpora  quadri- 
gemina  as  the  "nates"  and  "testes,"  the  suggested  resemblance  of  the  corpora  mamil- 
laria  to  the  female  breasts,  of  the  calcar  avis  to  the  cock's  spur,  of  the  lyra  Davidis  to 
a  harp,   or  of  the_  fornix  to  an  arch. 

In  order  to  render  more  exact  investigation  possible,  the  pioneer  observers  first 
sought  to  overcome  the  softness  of  the  central  nervous  substance,  and  to  that  end  employed 
various  chemical  agents,  as  alcohol,  corrosive  sublimate  and  salt  solutions.  Cold  was 
also  used  to  give  the  brain  greater  consistence,  and,  indeed,  Gennari  and  Reil  made  their 
observations  on  frozen  brains.  In  this  manner,  in  a  purely  morphological  way,  began  the 
foundation  of  the  study  of  the  internal  connection  of  the  individual  brain-segments  and. 
until  the  middle  of  the  nineteenth  century,  the  method  of  direct  mechanical  dissociation 
of  the  alcohol-hardened  brain  was  employed  to  demonstrate  the  chief  fibre-tracts  (Gall 
and  Spurzheim,   Burdach,   Reil,  Arnold,   Foville). 

A  distinct  advance  in  brain-anatomy  was  made  when  the  structure  of  the  central 
nervous  system  began  to  be  studied  from  the  standpoint  of  development.  In  this  Tiedemann 
and  Reichert  were  pioneers.  In  the  introduction  to  his  "  Anatomie  und  Bildungsgeschichte 
des  Gehirns,"  Tiedemann  observes  that  the  origin  and  development  of  the  brain  were  an 
almost  totally  neglected  part  of  anatomy  and  physiology.  He  mentioned  the  law  formu- 
lated by  Harvey,  that  the  embryo  of  man  and  of  the  animals  does  not  appear  in  a  com- 
pleted and  only  diminished  form,  but  that  it  begins  with  a  simpler  form,  successively 
passes  through  lower  formative  stages  and  finally  reaches  a  higher  stage  of  development. 
Why,  says  Tiedemann,  should  not  a  similar  progression  from  a  simpler  to  a  more  complex 
structure  also  occur  in  the  construction  of  the  brain  of  the  embryo  and  of  the  fcetus ; 
and,  further,  should  not  this  process  supply  explanations  concerning  the  form  and  struc- 
ture of  the  brain,  so  intricate  in  its  completed  condition?  Tiedemann  busied  himself  for 
several  years  with  the  construction  of  the  embryonal  and  foetal  brain.  The  pure  mor- 
phology of  the  bfain,  however,  reached  high-water  mark  with  the  embryological  method 
of  examination  followed  by  C.  B.  Reichert.  Through  the  work  of  Schmidt,  Mihalkovics, 
KoUiker,  His  and  others,  this  method  has  led  to  a  strict  scientific  division  of  the  brain 
and  to  the  establishing  of  a  comprehensive  morphological  basis. 

7  97 


^8  THE    FIBRE-TRACTS. 

By  these  "  embryological "  methods  much  was  gained,  but  by  no  means  all. 
Embryology  taught  us  to  understand  the  development  of  the  form,  but  told  us  nothing 
concerning  the  intimate  connection  of  the  parts,  a  clear  insight  into  which  alone  leads  to 
a  comprehension  of  the  function  of  the  central  nervous  system.  The  question  of  the  intimate 
connection  of  the  parts,  however,  is  nothing  but  the  question  of  the  fibre-tracts  and  there- 
with we  enter  a  new  phase  of  brain-investigation.  We  may  designate  this  phase  as  the 
physiological  in  contrast  to  the  pure  morphological,  since  the  extraordinarily  difificult  and 
laborious  endeavors  of  the  later  investigators  to  unravel  the  intricate  fibre-complex  of  the 
central  nervous  system  are  all  undertaken  from  the  physiological  standpoint  and  with  a 
physiological  aim. 

After  Helmholtz  had  shown  for  the  invertebrates  and  Remak  for  the  ^'ertebrates, 
that  the  nerve-fibres  proceed  from  the  nerve-cells,  it  became  evident  that  the  simple 
method  of  dissociation  no  longer  sufficed.  What  neurology  had  then  to  attempt  was 
not  merely  the  accurate  description  of  the  external  form,  but,  before  all  else,  the  estab- 
lishing and  the  tracing  of  the  intricate  paths  which  the  nerve-fibres  pursue,  and  the  definite 
establishment  of  all  the  numerous  connections  joining  centre  with  centre  within  the  interior 
of  the  central  nervous  system  and  bringing  the  latter  into  relation  with  the  periphery. 
Although  tracing  these  fibre-paths  even  within  the  peripheral  nerves  is  by  no  means  easy 
because  of  the  peculiar  plexus-formation  and  anastomoses  of  certain  nerves,  such  task  is 
especially  difficult  within  the  brain  and  spinal  cord,  since  here  often  within  a  small  space 
the  most  diverse  paths  run  side  by  side  and,  further,  decussations  and  interfeltings  of  the 
nerve-fibres  make  the  direct  tracing  of  the  nerve-tracts  impossible. 

A  method  of  fundamental  unportance  for  following  the  nerve-paths  through  longer 
stretches  was  now  introduced,  namely,  the  method  by  series  of  consecutive  sections, 
introduced  by  Benedikt  Stilling.  The  necessity  of  cutting  the  brain  and  spinal  cord  into 
thin  segments  for  the  accurate  investigation  of  their  finer  structure,  even  the  older  inves- 
tigators recognized  and  suggested  means  by  which  to  accomplish  this  end.  As  early 
as  1824,  Rolando  made  thin  cross-sections  of  hardened  spinal  cord  with  a  razor  and 
examined  them  with  a  hand-lens.  But  the  segments  cut  by  Rolando  were  not  sufficiently 
thin  to  be  used  with  higher  amplification  ;  moreover,  they  were  made  without  system. 
In  1836  Valentin  examined  microscopically  the  spinal  cord  of  freshly-killed  sheep  and 
pigeons,  by  cutting  the  cord,  under  water,  with  a  pointed  two-bladed  knife,  into  the 
thinnest  possible  lamella  and  then  carefully  compressing  the  sections  while  being  observed. 
In  this  manner  Valentin  studied  the  spinal  cord  layer  by  layer,  from  without  inward,  in 
longitudinal  sections,  and  expressed  the  opinion,  that  for  the  correct  understanding  of  the 
structure  of  the  spinal  cord  examination  by  strata  is  the  only  proper  way.  Four  years 
later,  Hannover  advanced  along  this  line  even  farther  than  Valentin.  He  employed  a 
brain  and  spinal  cord  hardened  in  chromic  acid,  which  he  cut  into  thin  sections  with  a 
sharp  knife,  and  examined  the  relations  of  these  lamellae  piece  by  piece. 

Shortly  after  the  appearance  of  Hannover's  paper,  the  great  doctor  of  Cassel, 
Benedikt  Stilling,  began  in  1841  his  investigations  concerning  the  structure  of  the  spinal 
cord.  Stilling  was  the  first  to  cut  a  spinal  cord  into  many  consecutive  sections,  as  thin 
and  transparent  as  possible,  and  then  to  study  in  each  section  the  distribution  of  the 
white  and  gray  substance.  He  traced  progressively  from  section  to  section  the  changes 
in  the  picture,   and  finally,   by  reproducing   the    individual    pictures,   gained,   at  least  to  a 


METHODS    OF   INVESTIGATION.  99 

certain  degree,  a  clear  conception  of  the  internal  structure  of  the  cord.  This  method  by 
series  of  consecutive  sections,  which  Stilling  designated  as  "investigation  layer  by  layer," 
is  even  to-day  the  one  most  employed  in  the  e.xamination  of  the  central  nervous  system. 
During  the  continual  use  of  so  productive  a  method,  it  was  inevitable  that  the  original 
technique  of  Stilling  should  undergo  many  alterations  and  improvements.  The  employ- 
ment of  the  method  was  facilitated  by  better  hardening  of  the  organs.  Already  in  1832, 
Ludwig  Jacobson  recommended  potassium  chromate  as  a  preservative  for  anatomical 
preparations.  Hannover  first  put  Jacobson' s  discovery  to  use  for  histological  investigation. 
Later  chromic  acid  was  displaced  from  the  technique  by  one  of  its  salts.  At  any  rate, 
no  one  has  rendered  greater  service  than  Heinrich  Miiller  by  the  introduction  of  potas- 
sium bichromate,  now  so  universally  serviceable.  From  him  came  also  the  classic  Miiller' s 
fluid,  which,  indeed,  even  to-day  is  much  used  in  its  original  composition.  Later  followed 
many  new  hardening  reagents.  One  of  these,  formalin  or  formol,  must  be  especially 
mentioned,  since  in  recent  years  its  many  advantages  have  brought  it  into  universal  use. 
Formol  was  introduced  in  histological  technique  by  Blum  in   1893. 

The  method  of  cousecutive  sections  was  further  facilitated  by  the  introduction  of  the 
microtome,  by  which  e.xact  cutting  and  large  regular  sections  are  made  possible,  so  that 
an  entire  brain  may  be  laid  into  a  series  of  thin  sections  without  losing  one.  We  may 
mark  the  sections  in  their  proper  sequence,  determine  in  each  the  topography  of  the 
gray  substance  and  of  the  fibre-tracts,  and,  by  means  of  the  series,  from  these  isolated 
data  construct  a  composite  picture  of  the  principles  of  construction  of  the  part  of  the 
brain  under  discussion. 

The  application  of  Stilling' s  mode  of  investigation  was  materially  facilitated  by  the 
methods  of  staining.  For  a  long  time  Gerlach's  carmine  staining  was  dominant.  An 
important  advance  was  gained  by  Weigert's  admirable  hemato.xylin-method.  At  present 
we  have  at  our  disposal  a  quite  considerable  number  of  different  dyes,  which  may  be 
used  with  advantage  in  investigating  fibre-paths.  But  neither  the  Weigert  stain,  nor  any 
other  of  the  procedures  so  far  recommended  and  used,  is  capable  of  solving  the  question,  the 
answer  to  which  has  always  been  most  sought  for  the  correct  understanding  of  the  structure 
of  the  nervous  system.  Continually  was  asked  :  In  what  manner  are  the  nerve-fibres 
related  to  the  nerve-cells?  In  what  manner  are  the  nerve-cells  related  to  one  another? 
How   do    the    nerve-fibres    in    the   brain    and    spinal    cord    arise  and    how   do    they  end  ? 

In  this  connection,  two  methods  were  epoch-making — Ehrlich's  methylene  blue  7netliod 
and  Golgi's  silver-method.  Ehrlich's  procedure,  which  was  introduced  in  i886  and 
depends  on  the  coloring  of  the  living  nerves  by  means  of  methylene  blue,  was  subse- 
quently improved  by  Retzius,  Apathy,  Bethe  and  others.  Golgi's  method  is  older.  A 
number  of  years  before,  the  Italian  investigator  had  obtained  preparations,  in  which  the 
nerve-cells  and  their  processes  stood  out  with  great  sharpness  as  dark  figures,  by  treating 
the  brain-substance  with  the  chromic  acid  salts  and  with  silver  nitrate.  Golgi  described 
his  method  as  early  as  1873,  but  at  first  his  observations  were  little  known.  Not  until 
the  publication  of  an  elaborate  paper  in  1886,  did  Golgi  excite  widespread  attention  and 
his  results  and  methods  become  the  starting  point  of  an  energetic  examination  of  the 
central  nervous  system.  For  example,  the  Spanish  savant,  Ram6n  y  Cajal,  was  able,  by 
the  use  of  the  Golgi  method  on  embryos  and  young  animals,  to  arrive  at  results  that 
partly  solved  many  of   the  dominant  questions,  or  placed  them  in  a  new  light.       At  first 


loo  THE    FIBRE-TRACTS. 

through  the  labors  of  this  investigator,  soon  also  through  those  of  others,  especially  of 
Kolliker,  Lenhossek,  van  Gehuchten  and  Retzius^  a  clear  picture  took  the  place  of  the 
previous  schemata.  The  most  important  findings  of  these  researches  are,  that  the  nerve- 
fibres  are  nothing  more  than  extraordinarily  long  processes  of  the  nerve-cells,  that  every 
nerve-fibre,  from  beginning  to  end,  is  to  be  regarded  as  a  part  of  a  single  nerve-cell, 
and  that  every  nerve-cell,  with  the  nerve-fibres  proceeding  from  it,  represents  an  histo- 
logical individuality  or  nervous  unit.  Waldeyer  christened  such  anatomical  unit,  neurone, 
and  therewith  founded  the  neurone-theory. 

The  method  of  Stilling  enables  us  to  trace  a  nerve-tract  through  a  long  stretch. 
The  identity,  however,  is  possible  and  certain  only  so  long  as  the  fibre-bundles  compos- 
ing the  tract  do  not  suffer  interruption,  or  so  long  as  they  are  not  deflected  from  the 
plane  of  the  section,  or  do  not  separate  into  widely  diverging  fibres.  The  accurate  iden- 
tification and  tracing  of  the  fibre-tracts,  even  when  they  branch  in  the  most  diverse 
directions  or  resolve,   have  necessitated  the  search  for  new  methods. 

One  of  these  additional  methods  is  the  pathologico-anatoniical  one,  based  on  the  inves- 
tigation of  secondary  degenerations.  Rokitansky  announced  in  the  first  edition  of  his 
Pathological  Anatomy  (1847),  that  atrophy  of  the  brain  following  apoplexy  and  inflam- 
mation leads  to  atrophy  of  different  fibre-paths,  when  extensive,  indeed,  to  the  disap- 
pearance of  an  entire  hemisphere  and  the  related  fundamental  tracts.  This  communica- 
tion for  a  time  remained  unnoticed.  In  1S50  Ludwig  Tiirck  described  more  closely  such 
secondary  degenerations  and  inferred  from  his  findings,  that  in  those  cases  of  cross-section 
of  the  spinal  cord,  in  which  the  direction  of  physiological  conductivity  and  that  of  the 
degeneration  were  identical  in  the  secondarily  degenerating  cord-paths,  the  degeneration 
itself  was  caused  by  the  disturbance  of  functions.  Notwithstanding  these  exceedingly 
important  results,  ai  first  only  few  investigators  followed  Tiirck  along  this  line  of  investi- 
gation. In  later  years,  however,  this  method  has  been  universally  employed  and  to  it 
we  are  indebted  for  the  many  papers  by  which  our  knowledge  of  the  fibre-paths  of  the 
central  nervous  system  has  been  materially  extended.  The  method  depends  upon  the 
principle,  that  every  nerve-fibre  in  its  function  is  dependent  upon  the  related  nerve-cell. 
Destruction  of  the  latter,  or  separation  of  the  nerve-fibre  from  its  cell,  results  in  degenera- 
tion of  the  related  fibre.  Let  us  assume  that  a  descending  tract  of  the  spinal  cord  has 
been  destroyed  in  some  part  of  its  course.  What  happens  ?  The  portions  of  the  nerve- 
fibres  below  the  injury  are  separated  from  their  trophic  centre  ;  they  therefore  die.  This 
destruction  or  secondary  degeneration  within  the  spinal  cord  proceeds  downward.  On 
examining  a  cross-section  of  the  cord  passing  below  the  seat  of  injury  and  comparing  it  with 
a  corresponding  section  of  a  normal  spinal  cord,  the  seat  of  the  degeneration  is  readily 
located    and    the  involved  tracts  may  be  accurately  followed  by  means  of   serial  sections. 

This  method  of  investigation  by  secondary  degeneration  is  closely  related  to  the 
physiological  method  or  the  method  of  vivisection.  Certain  nerve-centres  or  nerve-fibres 
of  an  animal  may  be  directly  stimulated  or  destroyed,  and  from  the  resulting  symptoms 
conclusions  drawn  as  to  the  relations  of  the  nerve-centres  or  nerve-tracts  to  the  peripheral 
parts  ;  thereby  a  functional  differentiation  of  the  nerve-fibres  is  also  possible. 

The  pathological  method  is  based  on  a  principle  similar  to  that  of  the  vivisection 
procedures.  Here  also  the  destruction  of  parts  of  the  central  nervous  system  is  con- 
cerned,   but    these    mutilations   are    not   experimental    but    caused   by    the    establishing    of 


METHODS    OF   INVESTIGATION.  loi 

diseased  processes.  Ln  this  relation,  the  study  of  the  patholos^ical  changes  in  certain 
affections  of  the  spinal  cord  is  of  primary  importance. 

By  means  of  the  experimental  tnethod,  which  has  been  used  on  animals  with  such 
great  success,  we  are  able  to  follow  and  to  study  the  course  of  the  fibre-bundles  by 
degenerations.  This  method,  employed  only  under  certain  conditions,  was  introduced  by 
Gudden  and  his  pupils  and  is  the  atrophy-method,  or  the  method  of  developmental 
arrest.  Gudden' s  method  is  distinguished  from  other  experimental  procedures  in  that  it 
is  directed  against  the  young  animal.  The  chief  difference  consists  therein,  that,  follow- 
ing an  experimental  impression  on  the  new-born  animal,  the  entire  process  proceeds  much 
more  rapidly  and  completely  than  in  the  adult.  The  absorption  of  the  disintegration 
products  from  the  elementary  parts  destroyed  goes  on  much  more  rapidly  and  com- 
pletely in  the  new-born,  so  that  scarcely  a  trace  of  the  fibres  and  only  few  remains  of 
the  cells  are  left.  In  addition,  the  technique  is  relatively  easy,  while  a  further  distinct 
advantage,  as  Gudden  himself  pointed  out,  is  the  almost  incredibly  rapid  and  admirable 
healing  of  the  injury  without  disturbing  secondary  processes. 

In  1852  Waller  showed,  that  the  peripheral  stump  of  a  cross-sectioned  peripheral 
ner\'e  undergoes  degeneration.  For  a  long  time  it  was  believed,  that  the  peripheral 
segment  alone  degenerated,  and  that  the  central  one  remained  unaffected  by  such  changes. 
Since  the  study  of  Ranvier  on  degeneration  and  regeneration  of  sectioned  nerves,  how- 
ever, we  know  that  also  the  central  segment  suffers  important  modifications.  Ranvier 
showed,  that  in  the  central  segment  of  the  axis-cylinder  new  fibrillae  were  formed,  which 
became  new  nerves,  using  the  sheath  of  the  degenerating  peripheral  segment  as  a  sup- 
port to  reach  the  periphery.  The  nerve  reassumes  its  function— it  is  regenerated.  If, 
however,  from  any  cause  the  developing  nerve  fails  to  secure  such  support,  its  further 
development  is  arrested  and  a  nervous  tumor,  a  neuroma,  is  formed,  as  seen  in  amputation- 
stumps.  But  in  these  cases,  especially  when  of  long  standing,  a  certain  grade  of  atrophy 
of  the  nerves,  as  well  as  a  diminution  in  the  number  of  the  corresponding  nerve- 
cells,  may  be  observed.  These  changes  are  exceptionally  rapid  and  marked  so  soon 
as  the  interference  occurs  in  young  individuals,  particularly  in  the  new-born.  If  in 
a  new-born  animal  a  motor  ner\'e  is  removed,  a  certain  region  of  the  cerebral  cortex 
destroyed,  or  the  spinal  cord  partially  cut  through,  not  only  is  always  a  degeneration  of 
the  fibres  \n  the  separated  peripheral  stump  to  be  observed,  but  also  atrophy  and  indeed 
complete  disappearance  of  the  cells  of  origin.  Gudden  believed  at  first,  that  this  differ- 
ence from  the  Wallerian  degeneration  was  attributable  to  the  lesion  being  in  the  new- 
born animal.  Later,  he  recognized  that  it  was  not  the  age,  but  the  position  that  exer- 
cised the  influence.  Then,  too.  Forel  proved,  that  the  death  of  the  cell  after  destruction 
of  the  related  fibre  occurred  in  the  adult,  as  well  as  in  the  new-born  animal.  Death  of 
the  cell  depends  alone  on  the  place  where  the  fibre  is  sectioned.  Section  of  a  motor 
nerve  at  the  periphery  is  followed  by  only  a  slow  impairment  and  diminution  in  the  size 
of  the  cells  and  fibres  (jf  the  central  stump.  Section  of  the  same  nerve  at  its  point  of 
emergence  from  the  brain,  results  in  the  death  of  the  central  root,  as  well  as  of  all  the 
cells  of  origin  within  the  nucleus  of  the  nerve.  The  method  of  Gudden  has  been  rich 
in  results.  In  1872-74  Gudden  proved,  by  extirpation  of  the  cortical  motor  zone  in 
dogs,  that  the  pyramidal  tracts  run  direct  from  the  cerebral  cortex  to  the  sjjinal  cord. 
Other    important    results   are   the   establishing    cjf    the    nuclei    of   origin    of    almost    all  the 


I02  THE    FIBRE-TRACTS. 

motor  cerebral  nerves,  the  course  of  the  medial  fillet  and  the  termination  of  the  optic 
tract.  Closely  connected  with  the  method  of  Gudden  are  the  pathological  cases  of  early 
lesion  and  consequent  atrophy  of  certain  parts  of  the  central  nervous  system,  as  well  as 
the  cases  of  congenital  malformation  involving  the  cerebro-spinal  axis. 

Our  knowledge  concerning  the  fibre-tracts,  moreover,  has  been  especially  advanced 
by  the  embryological  method  introduced  by  Flechsig,  based  on  the  study  of  the  develop- 
ment of  the  nerve-fibres.  This  method  rests  on  the  fact,  that  the  different  fibre-systems 
within  the  central  nervous  system  acquire  the  medullary  substance  at  a  definite  time,  which, 
however,  varies  for  the  individual  systems.  On  examining  the  infantile  brain,  it  is  found 
that  certain  fibres  are  already  medullated,  while  others  have  not  yet  acquired  this  sheath. 
This  difference  between  the  medullated  and  non-medullated  fibres  is  readily  appreciable 
microscopically  and,  therefore,  the  examination  of  the  nervous  system  in  its  various  develop- 
mental stages  affords  the  possibility  of  delimiting  and  tracing  certain  fibre-systems. 

An  additional  means,  which  has  contributed  much  not  only  to  the  morphology  but 
also  especially  to  the  accurate  investigation  of  the  fibre-tracts,  is  the  comparative  Miatoyn- 
ical  method.  Since  in  the  different  classes  of  animals  this  or  that  part  of  the  brain  is 
varyingly  developed,  in  correspondence  with  different  functional  development,  the  investi- 
gations in  the  domain  of  comparative  anatomy  have  supplied  numerous  explanations  con- 
cerning the  many-sided  connections  of  individual  parts  of  the  central  nervous  system. 

Finally,  a  combination  of  these  various  methods  has  been  attempted.  Edinger 
united  the  comparative  anatomical  method  and  that  of  Flechsig.  Bechterew  combined 
vivisection  with  the  study  of  development  and  created  the  embryologico-physiological 
-method.  Admirable  results  were  also  achieved  by  Bechterew  with  his  pathologico-physio- 
logical  method,  which  consisted  in  studying  secondary  degenerations  with  simultaneous 
stimulation  of  the  degenerated  parts  by  means  of  the  electrical  current. 


nally  by  the  cuticle-plate. 


HISTOGENESIS  OF  THE  NERVOUS  SYSTEM. 

The  elements  of  the  nervous  system  are  developed  from  the  outer  germ-layer  or 
the  ectoderm.  As  we  have  already  seen,  the  brain  and  the  spinal  cord  arise  from  a  broad 
medial  strip  of  ectoderm.  Here  the  medullary  plate  is  formed,  which  is  bounded  exter- 
The  medullary  plate  sinks  and,  at  the  same  time,  projects  with 
its  edges  above  the  level  of  the  embry- 
onic area ;  in  this  way  is  formed  the 
■)nedullary  groove,  bounded  by  the  vied- 
ullary  ridges.  The  medullary  groove 
closes  and  becomes  the  medullary  or 
neural   tube. 

The  medullary  tube,  the  direct 
successor  of  the  medullary  plate,  consists 
at  first  of  closely  pressed  epithelial  cells, 
each  of  which  extends  the  entire  thick- 
ness of  the  layer.  The  wall  of  the  entire  tube,  therefore,  originally  exhibits  the  character  of 
a  single-layered  columnar  epithelium,  whose  cells  are  bounded  by  the  membrana  limitans 
externa  on  the  one  side,  and  by  the  membrajia  limita7is  interna  on  the  other  (Fig.  97). 
Each  epithelial  cell  encloses  a  large  nucleus.     In  the  inner  zone,  other  large  cells  are  irregu- 


FlG.  97. — Dorsal  half  of  neural  tube,  overlaid  by  th 
epithelial  and  two  dividing  (so-called  germ-)  cells 


DEVELOPMENT  OF   NEUROGLIA.  103 

larly  scattered  between  the  epithelial  elements,  from  which  they  are  clearly  distinguished  by 
their  round  form  and  transparent  homogeneous  protoplasm.  His  designated  these  as  the 
germ-cells. 

The  epithelial  cells  multiply  rapidly  and,  consequently,  become  laterally  compressed 
and  elongated.  Their  nuclei  lie  at  different  heights  and  give  rise  to  the  appearance  of  a 
three-  to  six-celled  layer.  In  reality,  however,  the  cells  completely  retain  the  character 
of  a  single-layered  columnar  epithelium. 

Some  of  the  epithelial  cells  are  early  transformed.  They  grow  into  the  spongio- 
blasts of  His,  from  which  are  developed  the  supporting  elements,  the  cpendyma  and 
neuroglia  cells. 

Others  of  the  epithelial  cells  change  to  pear-shaped  elements  and  become  the  neuro- 
blasts,  which  are  transformed  into  the  nerve-cells. 

Both  kinds  of  cells,  the  spongioblasts  and  the  neuroblasts,  therefore,  are  derivatives 
from  the  original  ectodermic  elements  of  the  medullary  plate.  The  above  mentioned 
"germ-cells"  of  His  are  nothing  more  than  cells  of  the  primary  medullary  area  under- 
going mitosis  and  represent  elements,  whose  division  supplies  the  material  for  the  increase 
of  the  indifferent  ectodermal  cells,  on  the  one  hand,  and  of  their  derivatives,  the  spongio- 
blasts and  the  neuroblasts,   on  the  other. 

DEVELOPMENT  OF  THE   EPENDYMA   AND  THE   NEUROGLIA   CELLS. 

The  ependyma  cells  maintain  in  the  foetal  stage  the  character  of  an  epithelium 
and  the  relations  to  the  membrana  limitans  e.xterna  and  interna.  In  the  brain,  .as  in  the 
spinal  cord,  the  ependyma  cells  extend  from  the  inner  to  the  outer  surface  of  the  neural 
wall,  the  length  of  the  cells  keeping  pace  with  the  increase  in  the  tube.  The  inner 
portion  of  the  cell,  nearer  the  central  canal,  retains  more  the  character  of  a  cell-body — 
ependyma  cell,  while  the  outer  portion  gradually  diminishes  to  a 
delicate  fibre,  which  as  an  ependyma  fibre  radially  traverses  the 
neural  wall.  The  entire  arrangement  constitutes  the  ependyma 
system  or  the  ependyminm. 

On    examining   this    ependymal    framework    more    closely,   a 
distinctive  disposition  of   the  ependyma    cells  is  seen  in  the  spinal 


cord..  In  a  cross-section  of  the  medullary  tube  of  a  3-4  day  tion  of  neural  tube  of  a  four- 
chick  embryo  (Fig.  98 J,  we  recognize  how  the  ependyma  fibres  day  chick  embryo,  (/.en- 
traverse  the  wall  of  the  tube,   at  the  sides  passing  almost  parallel 

from  the  central  canal  and  ventrally  and  dorsally  diverging  radially.  In  conse- 
quence of  the  coming  together  of  the  nucleus-bearing  portions  of  the  cells,  there 
appears  within  the  medullary  tube,  in  the  vicinity  of  the  central  canal,  a  broad, 
richly  nucleated  zone,  the  inner  layer  of  His  or  the  ependymal  nuclei-zone  of  Len- 
hossek.  In  a  general  way,  this  zone  corresponds  to  the  later  epitheiulm  of  the  central 
canal.  The  ependyma  fibres  of  the  later  anterior  commissure  present  a  rough  appearance, 
being  heavy  and  beset  with  spines  ;  they  also  emphasize  the  already  slight  meridional 
disposition  of  the  more  laterally  situated  ependyma  fibres.  In  a  somewhat  later  stage, 
the  ependyma  fibres  exhibit  varicosities,  particularly  in  their  inner  portions  ;  in  addition, 
in  their  outer  portions  they  undergo  a  subdivision  into  several  branches,  all  of  which 
extend  to    the  periphery,   where  they  end  in  small  triangular  e.v])ansions. 


I04 


THE    FIBRE-TRACTS. 


Subsequent  stunting  of  the  lateral  parts  of  the  ependyma  framework  is 
most  marked  in  the  spinal  cord  of  the  higher  forms.  In  the  other  parts  of  the 
central  nervous  system,  the  ependyma  cells  and  fibres  retain  their  embryonal  form,  even 
after  completed  growth.  The  ependyma  cells  are,  therefore,  phylogenetically  as  well 
ontogenetically,    the    oldest  cells  of   the  supporting  framework,    arising  direcdy  from   the 

ectoderm  cells,  or,  indeed,  being  in  a 
modified  way  these  themselves.  During 
later  stages,  the  elements,  particularly 
the  ependyma  fibres,  are  curtailed  in 
varying  degrees  ;  a  part  of  the  epen- 
dyma cells  later  migrate  and  become 
the  neuroglia  cells. 

The  neuroglia  cells  arise  only 
after  the  formation  of  the  ependyma 
framework.  On  examining  the  spinal 
cord  of  a  ten-day  chick,  one  finds  a 
number  of  elements  which  closely  re- 
semble the  ependyma  cells,  their  fibres 
hkewise  extending  to  the  periphery  and 
there  ending  in  conical  thickenings. 
They  differ  from  the  ependyma  cells 
proper,  however,  in  that  their  cell- 
bodies  no  longer  lie  at  the  central  canal,  but  farther  outward.  At  first  such  cells  are 
encountered  only  in  the  vicinity  of  the  central  canal  and  in  meagre  number  : 
later,  however,  they  are  more  numerous  and  occur  also  in  the  peripheral  zone. 
This  is  explained  by  the  manner  in  which  the  neuroglia  cells  arise.  Originally  these 
cel.ls   lie,  as    do   the  ependyma    cells,   at  the    central   canal ;    then    the    cell-bodies    migrate 


-Transverse  section  of  the  spinal  cord  of  a  human  embryo, 
n.  long,  showing  ependymal  framework.     i^Lenhossck.) 


Fig.  100. — Development  of  the  neu- 
roglia cells.  Spinal  cord  of  a  ten-day 
chick.     (Lenhossek.) 


Fig 


cells 

,  the  white  substance  of 
pinal  cord  of  an  embryo  of 
n.  in  length.    (Lenhossek,) 


from  the  region  of  the  epithelium,  part  of  the  cell-body  becoming  a  thin  fibrilla,  that 
later  disappears.  Small  spines  and  branches  appear  on  the  former  smooth  cell-bodies, 
as  well  as  similar  thorny  outgrowths  for  a  short  distance  along  the  process  stretching 
from  the  cell-bodies  to  the  periphery.  At  first  such  migrated  cells  are  present  only  in 
sparing  number ;  later,  however,  their  number  materially  increases  and  the  cells  are  dis- 
tributed more  or  less   uniformly    throughout  the    entire    cross-section   of   the  spinal   cord. 


DEVELOPMENT  OF   NERVE-CELLS. 


105 


Fig.  102. — Transverse  sec- 
tion of  the  spinal  cord  of  a 
four-weeks  human  embryo. 
Differentiation  into  the  inner 
layer,  next  the  lumen  of  the 
canal,  the  middle  or  mantle 
layer,  containing  the  neuro- 
blasts, and  the  outer  periph- 
eral layer.  {His.) 


This  radiating  sustentacular  apparatus  constitutes  in  man  and  the  higher  mammal.i  an 
embryonal  feature.  Subsequently,  the  picture  changes.  The  radial  type  disappears  and 
the  shape  of  the  cells  alters.  The  minute  spicules  and  branches  develop  very  markedly, 
while  the  peripherally  directed  processes  atrophy.  The  cells  become  the  true  spi(/e>-  or 
Jicuroglia  cells.  The  latter,  therefore,  pass  through  various  developmental  stages;  at 
first  they  are  ependyma  cells,  then  radial  sustenacular  cells,  from  which  arise  the  neurog- 
lia cells. 

DEXELOPMENT   OF   THE   NERVE-CELLS. 

The  neuroblasts,  from  which  the  nerve-cells  arise,  are  developed  in  the  innermost  layer 
of  the  medullary  tube,  bordering  the  central  canal.      Thence  they  migrate  outward  through 
the  inner  layer  and  localize  within  a  dorso-ventrally  expanding  region,  that  is  bounded  medially 
by  the  hmcr  layer  and  laterally  by  the  margi7ial  zone.      On  e.xamining  a  cross-section  of  the 
medullary  tube  of  a  four-weeks  human  embryo  (Fig.  102),  the  cleft- 
like central  canal  is  seen  in  the  middle,  bordered  by  the  inner  plate, 
outside  of  which  lies  the  stratum 
of  neuroblasts,    broad    ventrally 
and   thinner   dorsally.       Follow- 
ing His,  we  call  this  .stratum  the 
mantle   layer.      Peripheralward, 
the  latter  joins  the  marginal  zone 
— the  Randschleier  of  His. 

The  neuroblasts  are  pear- 
shaped  cells,  with  oval  nuclei, 
which  send  out  a  peripherally  di- 
rected process  that  bears  at  its 
end  a  characteristic  thickening, 

the  growth-wedge  of  Cajal.  This  process  is  nothing  less  than  the 
later  nerve-fibre.  While  the  rapidly  growing  fibres  endeavor  to 
reach  their  objective  point,  the  cells  change  their  form.  On  the  surface  appear  small 
humps  and  jagged  protuberances.  These  projections  later  elongate  and  become  compact 
branches  beset  with  small  knobs.  By  the  further  development  of  the  knobs  and  the  manifold 
division  of  the  outgrowths,  the  later  protoplasttiic  processes  or  deiidrites  of  the  cells  arise. 
In  this  manner  the  nerve-cell,  or  rather  the  neurone,  is  formed  as  an  independent  individual. 
It  includes  the  cell-body  and  the  outgrowing  protoplasmic  processes  or  dendrites  and  sends  out 
the  delicate  netve-process  or  neurite,  which  in  its  later  development  becomes  the  nerve-fibre. 

DEVELOP.MENT   OF  THE  CELLS  OF  THE  CEREBRO-SPhM.^L   G.'WCLLA.    AND   THE 
SYMPATHETIC   GANGLIA. 
The  spinal   ganglia  are  developed  from  a  band  of   cctodermic  cells  located  where 
the  medullary  plate  passes  into  the  cuticle-layer.      In  the  stage  of  the  medullary  groove, 

this  gang  lion- sir ayid  occupies,  on  each  side,  the 
prominent  ridge  of  the  medullary  plate  and,  as 
the  medullary  tube  separates  from  the  overlying 
ectoderm,  unites  temporarily  with  the  strand  of 
the  other  side  to  form  a  common  medial  cord. 
In  consequence  of    the   formation   of    the    nu-dul- 


FiG.  103. — Further  development  of  the 
euroblasts.  On  the  right,  two  neuroblasts 
xhibit  processes  bearing  growth-wedges. 


Sflnal  ganglion 
CnttrU-ptate 

MtduUary  tube 

Pig. 


104.—  Development    of    the    ganglion-Rtrand. 
Schematic. 


io6 


THE    FIBRE-TRACTS. 


lary  tube,  the  elements  of  the  gangHon-strand,  the  gajiglioblasts,  are  displaced  laterally 
and  form,  on  each  side  of  the  medullary  tube,  segmentally  arranged  cell-groups.  The 
latter  are  the  anlagen  of  the  future  spinal  ganglia.  During  their  migration  along  the 
medullary  tube,  the  ganglioblasts  become  spindle-shaped.  This  form  becomes  subse- 
quently still  more  pronounced,  each  of  the  two  pointed  ends  gradually  growing  out 
into    a    nerve-fibre,     the    centrally    directed    one   growing    into   the  dorsal   portion  of   the 


Posterior  root 


Anterior  ; 
IG.  105. — Neuroblasts  and  ganglioblasts. 

cord  as  a  posterior  root-fibre,  and  the  other,  as  the  peripherally  directed  sensory  fibre, 
traversing  the  body  to  its  termination.  The  bipolarity  of  the  ganglion-cells  later  disappears, 
the  cells  becoming  unipolar  elements.  This  unipolarity  is  manifested  not  only  by  the  cells  of 
the  spinal  ganglia,  since  the  cells  of  the  corresponding  ganglia  of  the  cerebral  nerves  are  also 
unipolar  elements.      The  ganglion  acustici  alone  contains  permanently  bipolar  cells. 

The  sympathetic  ganglia  originate  from  the  cerebro-spinal  ganglia.  According 
to  the  younger  His,  this  development  is  accomplished  by  an  actual  migration  of  cellular 
elements  from  the  spinal  ganglia. 


THE   FORMED   ELEMENTS   OF  THE    NERVOUS  SYSTEM. 

The  formed  elements  of  the  nervous  system  are  the  support- cells  and  the  nerve-cells. 
A.    THE    SUPPORT-CELLS. 
These    include    the  ependyma    cells   and   the   neuroglia  cells.     The  former  constitute 
the  epithelial  lining,  the  epe7idy?na,  of  the  central  canal  and  its  prolongations — the  fourth 
ventricle,   the  aquaeductus   cerebri,   the  third  ventricle  and  the 
lateral  ventricles. 

The  neuroglia   cells,   the  spider  cells  or  astrocytes,  are 
present  in  all  parts  of  the  gray  and  white  substance  and  form, 
by  means  of  their  numerous  processes,  the  framework  proper, 
the  astropilemma  or  spo7igiopilemma.      As  chief  forms,  we  dis- 
tinguish the    short-rayed    and    the    long-rayed    neuroglia    cells. 
They  all    possess    numerous    processes,    which,    however,    are 
seldom  uniformly  distributed   around  the   circumference  of  the 
cell-body,  but  usually  emerge  in  separate  close  tufts,  like  bun- 
dles of  rays.     The  processes  are  delicate,  mostly  of  the  same 
thickness,  from  beginning  to  end  of  uniform  width  and  end  free.      While  in  the  majority 
of   cells   they  proceed   in  all   directions,   there  are  also  astrocytes  in  which  the  processes 
exhibit  a  one-sided  development,  or  arise  from  the  two  poles  of  the  cell. 


Fig.    106. — Neuroglia    cells    fro: 
the  human  cerebral  cortex. 


THE   NERVE-CELLS.  107 

For  a  long  time  the  supporting  tissue  proper  of  the  nervous  system,  or  the  neu- 
roglia, as  distinguished  from  connective  tissue,  blood-vessels  and  lymphatics,  was  regarded 
as  a  sort  of  ground-substance  in  which  the  nerve-cells  and  nerve-fibres  were  embedded. 
The  chief  role  therein  was  played  by  a  kind  of  cement-substance,  the  glia,  to  which  be- 
longed special  cells  and  fibrous  elements,  the  glia  cells  and  glia  fibres.  In  181 1  Keuffel 
first  succeeded  in  demonstrating  a  definite  meshwork  in  cross-sections  of  the  spinal  cord, 
by  brushing  out  the  nervous  substance,  and  believed  that  this  reticulum  represented  noth- 
ing more  than  the  prolongations  of  the  pia  mater.  Arnold  and  Virchow  termed  the  neu- 
roglia a  granular  ground-substance,  but,  as  early  as  1853,  Virchow  demonstrated  round 
or  fusiform  cells  within  this  ground-mass  and  regarded  the  tissue  as  of  nervous  character, 
believing  that  the  nerve-cells  were  developed  from  the  neuroglia.  Bidder  went  somewhat 
further  and  spoke  of  fibrillae  and  stellate  cells  with  processes.  In  1863  Kolliker  pointed 
out  that  the  supporting  tissue  of  the  nervous  system  consisted  of  nothing  else  than  a 
complex  of  anastomosing  stellate  cells,  which  by  their  union  formed  a  reticulum  for  the 
nervous  elements.  He  still  assumed,  however,  an  anastomosis  between  the  processes  of 
the  cells.  It  remained  for  Deiters,  by  means  of  isolation,  to  represent  the  neuroglia  cells 
in  their  correct  form.  The  greatest  service,  however,  was  rendered  by  Golgi.  Through 
his  investigations,  it  became  clear  that  the  neuroglia  is  not  a  special  issue,  but  that  it  is 
represented  by  certain  elements — the  neuroglia  cells,   spider  cells  or  astrocytes. 

B.    THE    NERVE-CELLS. 

The  first  accurate  description  of  the  nerve-cell  was  given  by  Remak  in  1838. 
Thirteen  years  later,  R.  Wagner  discovered  in  the  nerve-cells  of  the  electrical  lobes  in 
the  brain  of  torpedo,  that  of  the  processes  passing  out  from  the  cells  only  a  single  one 
is  connected  with  a  nerve-fibre.  In  1854  Remak  communicated  similar  results  in  his 
studies  on  the  nerve-cells  of  the  gray  ventral  columns  of  the  spinal  cord  of  the  ox. 
These  observations  of  Wagner  and  of  Remak  were  confirmed,  in  1865,  by  Deiters'  in- 
vestigations on  the  human  brain  and  spinal  cord.  Deiters  found  that  among  the  many 
processes  passing  from  a  nerve-cell  always  one  ran  unbranched,  while  the  others  under- 
went repeated  division.  The  unbranched  process  he  named  the  nerve-process  or  axis- 
cylinder  process,  and  the  branched  ones  the  protoplasmic  processes.  In  his  investigations 
Deiters  employed  the  method  of  isolation,  this  teasing  method  being  subsequently  long 
used  to  demonstrate  the  nerve-cells.  It  is  evident,  however,  that  with  such  technique, 
by  which  the  cells  were  torn  from  all  their  relations,  other  investigators  could  achieve 
little  more  than  Deiters  had  already  done,  and  that  the  most  diverse  statements  concern- 
ing the  conception  of  the  relations  of  adjacent  elements  to  each  other  were  inevitable. 
Thus,  a  direct  union  of  neighboring  cells  with  each  other  was  accepted  by  many  investi- 
gators as  an  undoubted  fact.  Sometimes  it  concerned  broad  connecting  bridges  or  anas- 
tomoses, sometimes  the  passage  of  delicate  end-fibres  into  each  other.  According  to 
other  investigators,  all  nerve-cells  possessed  more  than  a  single  typical  nerve-process. 
Gerlach's  work  merits  the  greatest  consideration.  Gerlach  succeeded  in  demonstrating 
an  exceptionally  rich  felt-work  of  the  most  delicate  nerve-fibres  in  all  parts  of  the  gray 
substance.  He  extended  the  observations  of  Deiters,  who  had  seen  the  protoplasmic 
processes  repeatedly  branch  and  also  the  most  delicate  of  these  ramifications  still  further 
subdivide,    in    that    he    held,  that    the    finest    ramifications    of    the    protoplasmic    processes 


io8  THE    FIBRE-TRACTS. 

eventually  formed  a  delicate  "nerve-fibre  reticulum."  This  Gerlach  regarded  as  the  most 
important  constituent  of  the  gray  substance.  According  to  Gerlach,  the  divisions  of  the 
delicate  protoplasmic  processes  observed  by  Deiters  were  only  the  beginning  of  the  ner- 
vous reticulum.  Gerlach,  however,  went  still  further.  He  assumed  that  from  this  net- 
work of  nerve-fibres,  by  the  gradual  confluence  of  the  minute  branches,  broader  nerve- 
fibres  were  again  formed,  which  emerged  from  the  gray  substance.  Accordingly,  the 
nerve-fibres  had  a  two-fold  origin,  on  the  one  hand,  directly  from  the  cells  as  nerve- 
processes  or  axis-cylinder  processes,  and,  on  the  other,  indirectly  from  the  cells  through 
the  medium  of  the  reticulum  of  nerve-fibres  resulting  from  the  branching  of  the  proto- 
plasmic processes.  Gerlach  supposed,  therefore,  that  the  end-twigs  of  the  sensory  fibres 
entered  the  dehcate  network,  which,  on  the  other  side,  received  the  branched  protoplas- 
mic processes  of  the  motor  nerve-cells.  Gerlach' s  fibre-reticulum  can  be  best  pictured  by 
comparing  it  with  the  capillary  network  of  the  blood-vessels ;  the  sensory  fibre  is  the 
artery,  which  is  resolved  into  the  capillary  network ;  the  protoplasmic  processes  of  the 
cells  form  the  beginnings  of  the  venous  reticulum,  from  which  proceeds  the  nerve-process 
representing  the  vein. 

This  nerve-fibre  reticulum  of  Gerlach  enjoyed  for  a  long  time  general  acceptance. 
With  the  improvements  in  the  methods  of  investigation,  however,  a  powerful  revulsion 
took  place.  In  this,  the  chief  r61e  was  played  by  the  silver-method  of  Golgi.  This 
investigator  made  the  important  discovery,  that  the  nerve-processes  of  the  cells,  regarded 
as  unbranched,  may  give  off  delicate  collateral  branches.  Moreover,  that  there  are  many 
cells  in  the  brain  and  spinal  cord  whose  nerve-processes  are  not  continued  as  meduUated 
nerve-fibres,  as  in  the  case  of  the  other  cells  and  in  conformity  with  the  general  law 
announced  by  Deiters,  but  resolve  into  their  ultimate  end-twigs  immediately  after  emerg- 
ing from  the  cells  or  after  a  short  course. 

Golgi  divided,  therefore,  the  nerve-cells  of  the  brain  and  the  spinal-cord  into  two 
classes :  Type  I,  cells  with  long  nerve-processes,  which  latter  are  directly  prolonged  into 
nerve-fibres  ;  Type  II,  cells  with  short  nerve-processes,  which  after  a  short  course,  almost 
immediately  after  e.xit  from  the  cells,   break  up  into  their  terminal  branches. 

Later,  the  two  varieties  were  described  as  the  types  of  Deiters  and  of  Golgi.  Also 
functionally  these  two  cell-types  differ.  Golgi  regarded  the  Deiters  cells  as  motor  and 
the  others  as  sensory  elements.  He  interpreted  the  protoplasmic  processes  as  merely  the 
nutritive  organ  of  the  nerve-cell  and  questioned  their  nervous  significance.  Of  most 
importance,  however,  is  the  hypothesis  advanced  by  Golgi  and  his  pupils  concerning  the 
internal  connection  of  the  central  nervous  apparatus.  Golgi  denied  anastomoses  of  the 
protoplasmic  processes  with  one  another  and,  consequently,  a  connection  between  the 
cells  in  the  sense  of  Gerlach,  although  suggesting  a  view  somewhat  similar.  He  cham- 
pioned the  existence  of  a  "general  nervous  network,"  which,  on  the  one  hand,  arises  from 
the  delicate  collateral  branches  of  the  long  nerve-processes  and  from  the  terminal  subdi- 
visions of  the  nerve-processes  of  cells  assumed  by  him  to  be  sensory  elements,  and,  on 
the  other  hand,  receives  additional  constituents,  such  as  the  end-twigs  of  the  nerve-fibres 
which  enter  the  gray  substance.  This  network  he  believes  to  e.xist  throughout  the  entire 
gray  substance  of  the  spinal  cord  and  of  the  brain. 

Opposed  to  this  "nervous  network"  are  the  important  considerations  of  His  and 
of   Forel.      As   early  as    1883,   based    upon    embryological    investigations.    His    had    shown 


THE    NERVE-CELLS. 


109 


the  independence  of  the  nerve-cells  from  one  another  ;  while  in  1887,  chiefly  upon 
pathological  experiences  with  Gudden's  atrophy-method,  Forel  opposed  the  acceptance  of 
a  general  network.  What  he,  for  the  first  time,  especially  emphasized,  was  the  principle 
of  contact  instead  of  continuous  reticular  connection.  There  was  still  wanting,  however, 
the  histological  proof,  and  this  proof  was  supplied  by  the  Spanish  savant,  Ramon  y  Cajal. 
By  means  of  his  investigations,  it  was  established  that  every  nerve-cell,  with  its  emerg- 
ing nerve-fibres,  represented  an  histological  as  well  as  a  neurological  entity — a  neurone, 
— and  that  the  entire  nervous  system  is  built  up  of  such  nervous  units. 

Closer  examination  of  such  a  nervous  unit  or  neurone  (Fig.  107),  shows  that  two 
kinds  of  processes  leave  the  cell-body:  («)  the  hx2ir\c\im<^  protoplasmic  processes  or  the 
dendrites  and  {b')  the  axis-cylinder  process,  also  called 
the  nerve-process,  axone  or  7ieurite.  The  nerve-process 
is  distinguished  by  its  uniform  diameter  and  smooth, 
regular  structure.  During  its  course  it  gives  off  many 
secondary'  twigs,  the  collaterals  ox  par  axone  s,  and  ends 
by  forming  a  terminal  arborization  or  tefodendrion.  All 
these  parts — the  cell  with  its  dendrites  and  the  axone 
with  its  telodendrion — constitute  collectively  a  nervous 
unit  or  a  neurone. 

Concerning  the  function  of  the  individual  parts  of 
the  neurone,  the  cell-body  with  its  dendrites  forms  the 
perceptive  and  impulse-giving  element,  while  the  nerve- 
process  with  its  collaterals  and  the  end -arborization,  is 
the  organ  of  transmission,  carrying  the  impulse  from  the 
nerve-cell  to  other  elements.  The  protoplasmic  proc- 
esses or  dendrites,  therefore,  conduct  cellulipetally, 
receiving  the  impulse  and  carrying  the  same  to  their 
own  cell-body  ;  the  nerve-process  or  neurite  conduct 
ccllidifugally,  receiving  the  nervous  stream  from  its 
own  cell-body  and  conducting  it  to  other  cells. 

The  manner  in  which  the  transference  from  one 
neurone  to  the  other  occurs  is  not  definitely  known. 
According  to  certain  investigators,  the  chaining  together 

of  the  nervous  units  is  effected  by  the  nerve-process  of  one  cell,  split  into  the  delicate 
fibres  of  its  end-arborization,  being  closely  applied  to  or  overlying  the  dendrites  and 
cell-body  of  another  cell,  whereby  the  transference  of  the  impulse  is  accomplished. 
The  opponents  of  the  theory  of  mere  contact  hold  that  there  exists  not  only  a  simple 
application,  but  also  a  continuous  connection  between  the  nervous  substance  of  the  nerve- 
processes  and  of  the  protoplasmic  parts  in  the  form  of  an  extremely  delicate  nervous 
network.  Even  if  definite  proof  were  supplied  as  to  the  connection  of  the  individual 
neurones  with  one  another  by  means  of  such  a  network,  it  remains  none  the  less  certain, 
that  the  nerve-cells  with  their  processes  are  the  essential  elements  for  the  entire  nervous 
activity  and  that  they  must  be  regarded  as  the  elements  of  the  nervous  system,  which 
anatomically,  trophically  and  as  regards  specific  function,  enjoy  a  certain  degree  of  indepen- 
dence.     We  are,   therefore,  justified    in    designating  them    as   nervous   units  or  neurones. 


TelodejtdrioK 


'. — Schematic   representation  of 


THE    FIBRE-TRACTS. 


The  nerve-cells  are  found  chiefly  in  the  central  nervous  system  ;  further,  in  the 
ganglia,  the  sense-organs  and  in  the  course  of  the  cerebro-spinal  and  the  sympathetic 
nerves.  They  are  of  variable  size  (4  to  135/^)  and  of  manifold  shape.  The  chief  charac- 
teristic of  every  nerve-cell  consists  in  its  always  possessing  processes.  Nerve- cells  with- 
out processes,  the  so-called  apolar  cells,  are  never  found  in  the  nervous  system  of  the 
adult.  Such  cells  are  either  immature  forms  and  found  only  during  the  earliest  period 
of  embryonic  development,  as  the  germ-cells  of  His,  or  they  are  artificial  products,  arising 
from  the  tearing  off  of  the  processes  during  isolation. 

According  to  the  number  of  the  processes,  unipolar,  bipolar  and  multipolar  cells 
are  distinguished. 


Fig.  108. — Nerve-cells  of  different  types. 


nipolar  cells;    b,  bipolar  cells;    c,  pyramidal  cell;    d,  Purkinje  cell. 


Unipolar  Cells.  These  are  numerous  during  embryonic  development,  as  the 
neuroblasts  ;  much  less  frequently  they  are  encountered  in  the  nervous  system  of  the 
adult,  as  in  the  retina  and  in  the  mesencephalon  on  each  side  of  the  aquaeductus  cerebri 
as  the  cells  of  origin  of  the  upper  motor  root  of  the  nervus  trigeminus.  The  nerve- 
cells  of  the  cerebro-spinal  ganglia  are  apparently  unipolar,  with  the  exception  of  the  cells 
of  the  ganglion  spirale  and  of  the  ganglion  Scarpae  ;  in  their  embryonic  condition,  how- 
ever, these  elements  are  bipolar,  only  later  becoming  unipolar,  when  their  nerve-processes 
divide,  at  a  certain  distance  from  the  cell-bodies,  into  a  central  and  a  peripheral  branch. 

Bipolar  Cells.  These  elements  are  found  almost  exclusively  in  the  peripheral 
sensory  nervous  system,  as  in  the  epithelium  of  the  olfactory  mucous  membrane,  in  the 
retina  and  in  the  spinal  and  vestibular  ganglia. 

Multipolar  Cells.  These  are  the  most  numerously  represented  and  the  most  impor- 
tant elements  of  the  nervous  centres.  Connected  with  these  are  two  kinds  of  processes — 
the   nerve-process,  axis-cyhnder  or  neurite,   and   the   protoplasmic  processes  or  dendrites. 


THE    NERVE-CELLS. 


Fig.  109. — Nerve-cell    from   spinal    cord   of 
born  cat. 


The  nerve-process  or  jicurite  is  usually  single,  although  cells  with  several  nerve- 
processes  occur  within  the  central  corte.x,  as  the  cells  of  Cajal.  To  this  category  belong 
also  the  multipolar  cells  of  the  sympatheticus  described  by  different  authors.  The  neurite 
leaves  the  cell  by  means  of  a  small  conical  elevation,  the  implajitation  C07ie ;  the  origin 
may  be  either  from  the  cell,  or,  as  is  very  often  the  case,  from  one  of  the  protoplasmic 
processes,  near  or  at  some  distance  from  the  cell-body.  Its  smooth  regular  quality  and 
uniform    diameter   throughout  its  entire  course  are  characteristic  of  the  nerve-process. 

The  protoplasmic  processes  or  the  dendrites  are  broad  and  dense  at  their  origin  from 
the  cell-body,  become  gradually  thinner  and  repeatedly  undergo  antler-like  division  to 
form    often    an    arborization  of  extraordinary  richness,  'the    finest  twigs  of  which  end  free. 

Their  irregular  course  and  knobbed  condition 
are  characteristic  of  the  dendrites,  which  are 
often  beset  with  numerous  knots,  thorns  or  spines. 
According  to  the  behavior  of  their  nerve- 
processes,  nerve-cells  are  grouped  into  two  classes. 

I.      Cells    'with    long 
nerve  -processes,      Deiters' 
cell-type     (Fig.     109),    in 
which    the    neurite    is    ex- 
tremely long  and  becomes 
the  axis-cylinder  of  a  cen- 
tral   or   peripheral    nerve- 
fibre. 
2.    Cells    u'ith    short    7ierve-proccsses,    Golgi's    cell-type   (Fig. 
no),    in   which    the    short    neurite    does    not    become    a    nerve- 
fibre,    but,    close    to    the    cell,    undergoes    repeated    division    and 

resolves  into  its  end-arborization.  These  elements  are  conveniently  designated  as 
Golgi  cells,  or  cells  of  Golgi's  Type  II,  as  distinguished  from  the  cells  of  Golgi's 
Type  I,  or  the  cells  with  long  neurites. 

According  to  the  behavior    of  the  protoplasmic    processes,   are  distinguished: 

a.  Stellate  cells,  the  dendrites  of  which  arise  separately  from  the  entire  circumfer- 
ence of  the  cell-body  and  extend  in  all  directions,  as  the  motor  anterior  horn-cells  and 
the  tract-cells  of  the  spinal    cord. 

b.  Cells  with  a  chief  dendrite,  in  which  a  robust  protoplasmic  process  arises,  along 
with  other  dendrites,  gives  off  lateral  branches  and  ends  arborized,  as  the  pyramidal  cells 
of  the  cerebral  cortex  and  the  mitral  cells  of  the  bulbus  olfactorius. 

c.  Cells  with  polar  dendrites,  in  which  the  cell-body  is  mostly  fusiform  and  gives 
off  from  opposite  sides  a  basal  and  an  apical  dendrite.  The  basal  dendrite  forms  a  tuft 
resembling  the  roots  of  a  tree,  while  the  apical  dendrite  springs  from  a  chief  protoplasmic 
process,  which  eventually  likewise  resolves  into  numerous  branches.  The  nerve-process 
springs  from  a  ba.sal  dendrite,  as  in  the  pyramidal  cells  of  the  hippocampus. 

d.  Cells  with  mo7iopolar  dendrites,  in  which  usually  several  chief  dendrites  arise 
from  one  pole  of  the  cell-body  and  soon  break-up,  after  repeated  division,  into  a  wide 
arborization.  The  nerve-process  arises  from  the  other  pole,  as  in  the  Purkinje  cells  of 
the  cerebellum,  or  in  the  granule  cells  in  the  gyrus  dentatus. 


Fig.  no.— Nerve-cell 
with  short  axone  or  nerve- 
process;  cerebral  cortex. 


THE    FIBRE-TRACTS. 


With  regard  to  their  intimate  structure,  the  nerve-cells  may  be  divided  into  two 
chief  groups,  in  accordance  with  the  behavior  of  their  protoplasm  towards  the  basic 
anilin  dyes.  Following  Nissl,  \Ve  distinguish  somatochromic  and  karyochromic  cells ;  in 
the  former  both  nucleus  and  protoplasm  stain,  in  the  latter  only  the  nucleus.  After 
staining  with  basic  anilin  colors,  such  as  methylene  blue  or  thionin,  the  protoplasm  of  the 
somatochromic  cells  exhibits  a  part  taking  the  dye,  the  cliromophilic  substance, 
and  a  part  remaining  uncolored,  the  chromophobic  substance.  The  stainable  part  appears 
as  a  multitude  of  deeply  colored  bodies  having  the  form  of  spherical  granules,  threads, 
flakes,  spindles  or  jagged  particles,  which  also  extend  into  the  dendrites,  but  do  not 
invade  the  axis-cylinder  process.      These  are    known    as  Nissl  bodies    or  granules.      On 


Fig.  III. — Structural  details  of  nerve-cells,  a,  pyramidal  cell  from  adult  huma 
network;  b,  pyramidal  cell  from  adult  human  visual  cortex;  c,  anterior  horn-cell  fr 
bodies;  d,  Golgi-Holmgren  canals  in  pyramidal  cell  of  rabbit;  e,  ending  of  nerve-f 
Golgi  network,     (a,  b,  d.  e,  and  /  after  Cajal;  c,  after  Schmaus.) 


motor  cortex,  showing  neurofibrillar 
m  human  spinal  cord  showing  Nissl 
arcs   on  nerve-cells;   /,  pericellular  or 


account  of  the  mottled  appearance  of  the  cell-body  conferred  by  the  staining  substance, 
von  Lenhossgk  calls  the  latter  tigi'oid.  The  arrangement  of  the  chromophilic  substance 
is  variable,  the  granules  sometimes  being  irregularly  scattered,  at  other  times  disposed 
in  concentric  layers,  or,  as  in  the  case  of  fusiform  cells,  grouped  as  a  sort  of  cap  at 
each  pole  of  the  cell-nucleus.  A  conical  mass  of  the  chromophilic  substance  is  usually 
found  at  the  points  of  division  of  the  dendrite-stems.  Concerning  the  chromophilic  part 
of  the  protoplasm,  the  nerve-Jibrillae  or  neurofibrillae  deserve  first  notice.  These  occur 
within  the  cell-body,  as  well  as  within  the  processes,  and  constitute  a  more  or  less  ex- 
tensive reticulum,  the  fibrillar  network.  In  Fig.  iii,  a  and  b,  such  intracellular 
networks  are  represented.  The  figures  e  and  f  show,  further,  how  nerve-fibres,  after 
resolving  into  delicate  arborizations,  end  at  the  cells  and  how  the  finest  fibres  form  a 
delicate  network  over  the  surface  of  the  cell-body  and  the  dendrites,  this  constituting 
the  external  network  of  Golgi. 


THE    NERVE-CELLS.  113 

The  chromophilic  and  the  chromophobic  substance  differ  also  in  their  functional 
relations.  The  chromophilic  substance  is  wanting  in  the  protoplasm  of  a  large  number 
of  nerve-cells  and,  therefore,  does  not  represent  a  vital  element  of  the  nerve-cell.  It 
accumulates  during  the  resting  condition,  is  sometimes  notably  reduced  during  the  period 
of  activity  and  disappears  in  lesions  of  the  neurone,  to  reappear  in  generous  quantity, 
however,  after  temporary  injury  and  recovery  of  the  cell.  These  characteristics  seem  to 
prove,  that  the  chromophilic  substance  exercises  a  nutritive  rather  than  a  nervous 
function.  The  chromophobic  substance  seems  to  represent  the  element  possessing  the 
function  of  conducting  the  nervous  stream,  the  fibrillae  and  the  perifibrillar  substance 
probably  sharing  in  this  conduction. 

In  addition  to  the  Nissl  bodies,  the  protoplasm  of  many  cells  contains  pigment 
granules,  which  are  usually  disposed  in  groups  t)f  variable  size.  The  pigment  is  com- 
monly not  uniformly  distributed  within  the  cell,  but  arranged  at  the  base  of  one  of  the 
dendrites.  It  is  wanting  during  early  life  and  increases  with  age.  Marinesco  regards 
the  pigment  granules  as  regression-  and  age-products  of  the  nerve-cells.  Claim- 
ing mention  are,  further,  the  fine  channels,  the  canals  of  Holmgren,  which  lie 
within  the  interior  of  the  cell  and  communicate  with  the  lymph-canals  situated  outside 
the  nerve-cell. 

The  nucleus  of  the  nerve-cells  appears  as  a  clear  spherical  vesicle,  possesses  a  distinct 
nuclear  membrane  and  lies  most  frequently  in  the  middle  of  the  cell.  Within  the  nucleus  are 
found  one  or  -several  deeply  staining  nucleoli,  which  often  contain  still  smaller  bodies, 
the  nucleololi.  The  remaining  interior  of  the  nucleus  is  traversed  by  a  meagre  sup- 
porting substance,  the  litiin  framework ,  on  v\hich  rests  the  chromatin,  as  well  as  against 
the   nuclear   membrane. 

Concerning  the  relations  of  the  cells  to  the  surrounding  tissue,  it  should  be  noted, 
that  the  cells  are  enclosed  within  cavities,  the  pericellular  spaces,  which  communicate  with 
the  perivascular  lymph-channels  of  the  central  nervous  system. 

The  envelopes  of  the  nerve-cells  are,  according  to  Cajal,  of  two  kinds.  («)  The 
cell-membrane  proper,  the  membrana  fundamental,  which  invests  every  cell  of  the  gray 
substance  as  an  extremely  delicate,  homogeneous,  elastic  cuticle,  and  (^b)  a  connective 
tisstie  envelope,  a  delicate  nucleated  membrane,  which  surrounds  all  the  peripheral  cells — 
ganglion  cells  and  the  cells  of  the  sympathetic — with  the  exception  of  the  cells  of  the 
retina  and  of  the  olfactory  mucous  membrane. 

The  ependyma  and  the  neuroglia  cells  are  sustentacular  elements  and  together  form 
the  supporting  framework  of  the  nervous  system. 

The  nerve-cells  are  usually  clo.sely  placed  in  larger  or  smaller  groups  and  consti- 
tute the  essential  components  of  the  gray  masses  of  the  nervous  system  ;  exceptionally 
they  occur  singly,  scattered  within  the  white  substance. 

The  nerve-fibres  are  the  axis-cylinder  processes  or  nerve-processes  of  the  nerve- 
cells,  and,  while  everywhere  encountered  within  the  gray  masses,  constitute  the  chief 
components  of  the  white  substance  of  the  nervous  system.  They  serve  to  establish  rela- 
tions of  the  nerve-cells  with  one  another,  whether  the  relations  be  between  neighboring 
or  widely  .separated  cells  of  one  ant!  the  same  region  of  gray  substance,  as  between 
the  various  regions  of  the  cerebral  cortex;  whether  the  relations  be  between  the  cells 
of   a  certain  region  and  those  of    one  far  remote,   as  between  the  central  cortex  and  the 


114 


THE    FIBRE-TRACTS. 


deeper  placed  gray  masses  (thalamus,  pons,  medulla  oblongata  and  spinal  cord) ;  or 
whether    the    relations    be    between    the    central    and    the    peripheral    nervous    system. 

The  nerve-cells  are,  therefore,  the  specific  function-bearing  elements.  They  are  the 
force-sources  or  the  transposition-apparatus  of  the  various  forms  of  nervous  activity  and, 
at  the  same  time,  also  the  nutritive  organs,  the  trophic  or  nutritive  centres,  of  the  nen^e- 
fibres  which  pass  from  the  cells.  A  nerve-fibre  separated  from  its  nutritive  centre  loses 
its  function  and  no  longer  conducts.  A  nerve-cell  with  its  protoplasmic  processes,  or 
dendrites,  and  its  nerve-process,  or  neurite,  constitutes  a  nervous  unit,  or  a  neurone. 
The  protoplasmic  process  conducts  cellulipetally  ;  the  nerve-process  conducts  cellulifugally 
and  through  it,  by  means  of  its  end-arborization,  as  well  as  of  its  collaterals,  occurs  the 
transference  of  the  impulse  from  one  neurone  to  the  other. 

Cells  of  the  same  function  usually  lie  together,  closely  packed,  and  constitute  a  region, 
a  centre,  a  ganglion  or  a  niLcleus.  In  like  manner  fibres  of  the  same  function  usually  He 
together,   closely  placed,   and  form  a  path  of  conduction  or  2t.  fibre-system. 


MICROSCOPIC  STRUCTURE  OF  THE  CEREBRAL  CORTEX. 

I.   CORTEX   OF  THE   PALLIUM. 

Based  on  the  arrangement  of  the  nerve-cells,  the  following  six  strata  or  layers  arc 
distinguished. 

I.  The  molecular  layer.  This  constitutes  the  most  superficial  stratum  and  is  a 
dense  feltwork,  composed  principally  of  fibres  running  mostly  parallel  to  the  surface ;  hence, 


/.  Moleatlar  laye. 


II.   Outer  gramde 
layer 


White  substance 


Fig.   112. — Schematic  representation  of  the  structure  of  the  cerebral  cortex. 


STRUCTURE  OF  CEREBRAL  CORTEX.  115 

it  is  also  designated  as  the  layer  of  tangential  fibres  or  the  tangential  fibre-layer.  In 
addition  to  numerous  neuroglia  cells,  this  layer  contains  the  terminal  ramifications  of 
the  dendrites  of  the  more  deeply  lying  pyramidal  cells  and  the  end-arborizations  of  the 
nerve-fibres  coming  from  the  white  substance  and  ending  in  the  cortex.  Further,  it  con- 
tains certain  cells,  including  medium  sized  polygonal  elements,  with  from  four  to  six 
dendrites  and  a  ner\'e-process  arborizing  within  the  molecular  layer,  and  fusiform  or  tri- 
angular cells,  with  few  more  or  less  horizontally  coursing  dendrites  and  two  or  several 
nerve-processes,  that  also  run  horizontally  and  end  within  the  molecular  layer.  The  ele- 
ments with  several  neurites  encountered  within  the  tangential  fibre-layer,  are  known 
as    Cajal  cells. 

2.  The  outer  granule  layer,  a  stratum  of  small  pyramidal  cells. 

3.  The  layer  of  small  and  medium  sized  pyramidal  cells. 

4.  The  inner  granule  layer,  a  stratum  of  small  pyramidal  cells. 

5.  The  layer  of  large  pyramidal  cells.  The  cell-body  of  the  pyramidal  cells  is. 
pyramidal  in  form,  the  base  presenting  towards  the  white  substance  and  the  apex  directed 
towards  the  molecular  layer.  The  apex  is  prolonged  into  a  robust  protoplasmic  process, 
the  primordial  branch,  which  gives  off  lateral  twigs  at  right  angles,  runs  toward  the 
molecular  layer  and  there  ends  after  repeated  division.  The  basal  dendrites  pass  off  from 
the  base  of  the  cell-body,  radiating  laterally,  or  towards  the  white  matter.  The  7ierve- 
process  springs  from  the  base  of  the  ceil,  or  from  a  basal  dendrite  close  to  the  cell-body, 
and  runs  towards  the  white  substance ;  during  its  course  through  the  gray  substance, 
the  nerve-process  gives  off  fine  collaterals,  that  run  horizontally  or  obliquely  and  end 
after  a  number  of  branchings. 

6.  The  layer  of  polymorphic  cells.  Here  are  found  cells,  ovoid,  fusiform, 
triangular  or  polygonal  in  form,  which  often  exhibit  a  robust  protoplasmic  process, 
directed  towards  the  molecular  layer.  Each  cell  sends  off  a  nerve-process  that  passes 
to  the  white  substance,  after  giving  off  a  number  of  collaterals.  Additional  cells,  with 
short  nerve-processes  or  of  Golgi's  II  type,  are  encountered,  not  only  in  this  layer,  but 
also  within  the  strata  of  small  and  large  pyramidal  cells.  Finally,  the  so-called  cells  of 
Martinotti  occur  as  fusiform  or  triangular  elements,  whose  distinguishing  characteristic 
consists  therein,  that  the  nerve-process  traverses  the  layer  of  the  pyramidal  cells  to  reach 
the  molecular  stratum,   where  it  ends. 

Regarding  the  disposition  of  the  nerve-fibres,  thicker  or  thinner  parallel 
bundles  of  fibres  enter  the  cortex  from  the  white  substance,  proceed  towards  the  periph- 
ery, and,  gradually  diminishing  in  thickness,  towards  the  layer  of  the  small  pyramidal 
cells  resolve  into  their  component  fibres.  These  bundles  are  known  as  the  medullary 
rays  or  radii  and  consist  of  the  nerve-processes  of  the  pyramidal  and  of  the  polymorphic 
cells,  which  are  passing  from  the  cortex,  and  of  the  nerve-fibres,  which  enter  from  the 
white  substance  and  end  within  the  cortex;  these  last  are  also  called  the  terminal  fibres. 
Between  the  individual  medullary  rays  are  narrow  interspaces  containing  delicate  horizon- 
tally coursing  fibres,  which  form  the  interradial  fcltwork.  The  latter  are  somewhat 
denser  where  the  medullary  radii  break  up  into  their  individual  fibres  and  thereby  pro- 
duce the  stripe  of  Daillarger.  The  fibres  of  the  interradial  ftltvvork  are  the  collaterals 
of  the  nerve-processes  of  the  pyramidal  cells.  Towards  the  periphery,  beyond  the  inter- 
radial feltwork  where  the  radii  resolve  into    their  .component  fibres,  lies   the   supraradial 


ii6 


THE    FIBRE-TRACTS. 


feltwork,  •  which  marks  the  ending  of  the  terminal  fibres    and,   farther   outward,   joins  the 
layer  of  tangential  fibres. 

The  cerebral  cortex  does  not,  however,  present  the  same  structure  in  all  regions. 
Local  variations  occur,  in  relation  to  the  arrangement  of  the  several  cell-la3fers,  as  well 
as  in    regard    to    the   behavior  of    the   fibre-layers.       There    exists   a   cyto-    and   a    myelo- 


''m 


w  i^'Vf  lir 


mm 


tii\fn 


2) 


Fig.  113. — Structure  of  the  cerebral  cortex  in  different  regions.  A,  cortex  of  precentral  convolution;  i?,  postcen- 
tral convolution ;  C,  superior  temporal  convolution  (auditory  cortex);  D,  surrounding  the  calcarine  fissure  (visual  cortex). 
(Caioi.) 

architectonic  differentiation,  the  recent  investigations  of  Brodmann  and  of  Vogt  having 
shown  that  the  entire  cerebral  cortex  may  be  subdivided  into  numerous  histologically 
different  cortical  fields.  While  it  is  impracticable  here  to  discuss  in  detail  the  differ- 
ences, Fig.  113  presents  these  relations,  so  far  as  the  make-up  of  the  cell-layers  is  con- 
rerned,  in  the  precentral'  and  postcentral  convolutions  and  in  the  auditory  and  visual 
cortical  areas,  according  to  the  earlier  studies  of  Ram6n  y  Cajal.     The  preponderance  of 


CORTICAL    AREAS. 


117 


the  large  and  giant  pyramidal  cells  in  the  precentral  convolution  is  to  be  noted  in  contrast 
to  the  peculiar   structure    of   the  visual  cortex,   in    which  the   original  six-layered   type  is 


Pig.   114. — Lateral  surface  of  hemisphere,  with  cytoarchitectonic  cortical  areas.     ( Brodmann.) 


Fig.  IIS- — Mesial  surface  of  hemisphere,  with  cytoarchitectonic  cortical  areas.     {Brodmann.) 


transformed  into  one  of  nine  layers,  by  the  introduction  of   special  layers  of   stellate  cells 
(Fig.    113,    I)  4  and   5;. 


ii8 


THE  FIBRE-TRACTS. 


II.   RHINENCEPHALON. 

Microscopic  structure  of  the  bulbus  olfactorius,  tlie  gyrus  fornicatus,  the  hippocampus 
and  the  gyrus  dentatus. 

Bulbus   Olfactorius. 

The  bulbus  olfactorius  exhibits  the  following  layers  : 

I.  The  layer  of  the  superficial  nerve-fibres.  This,  the  fibre-layer,  is  formed 
by  the  nerve-fibres  coming  from  the  olfactory  epithelium  (Fig.  ii6).  Within  the 
epithelium  of  the  olfactory  mucous  membrane,  the  bipolar  nerve-cells  lie  among  the  sus- 
tentacular  cells.      They  are  elongated  narrow  fusiform  or  irregular  elements,   with  a  thick 

peripherally  directed    process. 

Fibres  ending  in  iuUlls         Grannie  cells         Colgi  cells  that  gn^g  \vithin  the  epithelium, 

and  a  delicate  centrally  di- 
rected process,  beset  with 
varicosities,  that  traverses  the 
tunica  propria  undivided. 
United  into  small  bundles,  the 
fila  olfadoria,  the  central  fibres 
pass  through  the  apertures 
of  the  lamina  cribrosa,  enter 
the  bulbus  olfactorius  and 
there  form  a  close  feltwork  of 
crossing  fibres,  the  fibre-layer. 
2.  The  glomerular  lay- 
er. Joining  the  stratum  of 
nerve-fibres,  the  layer  of  glom- 
eruli olfactorii  follows.  Here 
the  end-arborizations  of  the 
fibres  from  the  fibre-layer  meet 
those  of  the  dendrites  of  certain 
cells,  namely,  the  brush  and 
mitral  cells.  In  consequence  of  the  close  intermingling  of  these  delicate  terminal  twigs,  small 
round  or  ovoid  structures,  the  glomeruli  olfactorii,  are  formed.  The  olfactory  fibres  com- 
posing the  fibre-layer  divide  often  into  two,  or  indeed  into  three,  twigs,  which  enter  the 
glomeruli  ;  in  this  manner,   such  ramifications  may  penetrate  into  two  different  glomeruli. 

3.  The  molecular  layer.  This  layer,  also  known  as  the  stratum  gelatinosum  of  Clarke, 
forms  a  stratum  comparable  to  the  layer  of  small  pyramidal  cells  of  the  cerebral  cortex. 
Within  it,  along  with  traversing  and  branching  fibres,  are  found  large  and  small  brush-cells. 

4.  The  layer  of  mitral-  cells.  When  compared  with  the  cerebral  cortex,  it  rep- 
resents the  layer  of  the  large  pyramidal  cells.  The  component  mitral  cells  are  of  quite 
characteristic  form.  The  cell-body  is  large,  exhibits  the  form  of  a  triangle  or  a  mitre, 
and  resembles  that  of  the  Purkinje  cells  of  the  cerebellar  cortex.  The  protoplasmic 
processes  are  of  two  kinds,  the  ordinary  dendritic  stems  and  the  so-called  olfactory 
brushes,  the  penicilli  olfactorii.      The  former  pass  obliquely  from  the  cells,  then  run  more 


membrane  and   bulbus  olfactorius.     Schematic 


GYRUS  FORNICATUS.  119 

horizontally,  branch  once,  and  end,  usually  after  a  long  course,  free,  forming  a  feltwork 
within  the  deepest  part  of  the  molecular  layer.  The  olfactory  brushes  traverse  tha 
molecular  layer  and  assist  in  forming  the  glomeruli  with  their  elaborate  varicose  end- 
arborizations.  The  nerve-processes  of  the  mitral  cells  extend  towards  the  granule-layer, 
bend  sagittally  at  various  levels  and  continue  within  the  tractus  olfactorius.  During  their 
course  they  give  off  collaterals,  which  end  in  free  branches  within  the  superficial  and  deep 
strata  of  the  molecular  layer. 

The  brush-cells  are  often  spindle-form  in  shape  and  horizontally  placed.  The  larger 
cells  are  found  within  the  molecular  layer,  external  to  the  mitral  cells,  which  latter  they 
in  general  resemble  in  giving  off  the  two  kinds  of  dendrites  and  in  sending  their  nerve- 
processes  to  the  granule-layer.  The  small  brush-cells,  also  known  as  the  peripheral  brush- 
cells,  lie  close  beneath  and  between  the  glomeruli.  They  likewise  send  one  dendrite  to 
the  glomerulus,   the  nerve-processes  behaving  like  those  of  the  large  brush-cells. 

5.  The  granule-layer.  Within  this  stratum  are  found  the  granule  cells  or 
granula,  peculiar  small  elements  with  long  processes.  These  granula  also  penetrate 
between  the  mitral  cells  and,  beyond  these,  into  the  molecular  layer  as  far  as  the  glom- 
eruli. The  granule  cells  are  triangular,  resembling  the  pyramidal  cells,  or  fusiform  or 
pear-shaped,  all  being  placed  vertically.  An  outwardly  directed  process,  mostly  single 
but  rarely  double,  divides  repeatedly  after  a  longer  or  shorter  course,  usually  close 
beneath  the  mitral  cells,  to  form  a  brush-like  terminal  arborization,  that  ends  within  the 
most  superficial  region  of  the  molecular  layer  at  the  glomeruli  in  delicate  filaments.  In 
the  opposite  direction,  that  is  inward,  the  granules  exhibit  several  processes,  which  are 
usually  smooth  and  slightly  branched  and  end  free  after  a  short  course.  As  yet,  a 
nerve-process  has  not  been  discovered.  In  addition  to  the  granules,  this  layer  contains 
cells  of  Golgi's  II  type — multipolar  elements  with  fusiform  or  polygonal  cell-body  and 
a  ner^^e-process  that  breaks  up  within  the  granule-layer.  The  nerve-fibres  running  within 
the  granule-layer  are  partly  the  nerve-processes  of  the  mitral  and  brush  cells ;  further, 
fibres  enter  the  bulbus  to  end  some  within  the  granule-layer,  and  some  within  the  molec- 
ular layer  in  the  vicinity  of  the  glomeruli,   after  having  penetrated  the  layer  of  mitral  cells. 

The  nerve-processes  of  the  mitral  and  brush  cells,  that  pass  to  the  tractus  olfacto- 
rius, end  within  the  cortex  of  the  tractus  and  of  the  tuberculum  olfactorium  and  within 
the  olfactory  area  of  the  substantia  perforata  anterior  and  the  adjoining  parts  of  the  sep- 
tum pellucidum.      These  end-stations  exhibit  the  structure  of  a   modified   cerebral   cortex. 

Gyrus  Fornicatus. 

The  structure  of  the  cortex  of  the  gyrus  fornicatus  deviates  from  the  typical  make-up 
of  the  cerebral  cortex  chiefly  in  relation  to  the  layer  of  the  large  pyramidal  cells.  Within 
the  gyrus  cinguli,  this  stratum  contains,  in  the  outer  half,  few  smaU  pyramid  cells  and, 
in  the  inner  half,  those  of  medium  size.  The  latter,  almost  all  of  uniform  diameter, 
lie  deeply  placed  and  together,  in  consequence  of  which  disposition  the  middle  portion 
of  the  layer  appears  poor  in  cells  and,  on  account  of  the  ascending  primordial  branches 
of  the  pyramidal  cells,  is  called  the  stratum  radiatum.  Towards  the  corpus  callosum, 
all  layers  suffer  diminution  in  thickness  and  in  the  size  of  the  cells.  The  cortex  of  the 
gyrus  hippocjimpi  bears,  in  many  respects,  a  close  resemblance  to  that  of  the  gyrus  cin- 
guli.   That  part  of  the  gyrus  hippocampi  which  borders  the  fissura  collateralis  and  rhinica. 


I20  THE    FIBRE-TRACTS. 

however,  exhibits  slight  deviation  from  the  common  type.  Towards  the  fissura  hippo- 
campi, the  molecular  layer  is  broader.  Within  the  layer  of  small  pyramidal  cells,  the 
cells  are  irregularly  arranged  in  chains  of  hillocks,  while  within  the  third  layer  are  found 
larger  pyramidal  cells  with  very  long  primordial  branches  ;  moreover,  of  these  cells  the 
largest  are  very  deeply  placed,  whereby  the  conspicuous  radial  striation,  the  stratum 
radiatum,  is  produced.  The  layer  of  polymorphic  cells  contains  almost  exclusively  small 
irregular  cells,  that  are  embedded  within  a  close  network  of  nerve-fibres. 

Hippocampus  and  Gyrus  Dentatus. 
The  hippocampus,  or  cormt  A7nmonis,  and  the  gyrus  dentatus  represent  two  spe- 
cial convolutions.  On  following  the  gyrus  hippocampi  dorsally,  one  reaches  the  subin- 
ciiltmi,  that  constitutes  that  part  of  the  hippocampal  convolution  in  which  gradually 
begins  a  change  in  the  structure  of  the  cerebral  cortex,  leading  finally  to  the  typical 
structure  of  the  hippocampus.  The  white  substance  splits  into  two  layers :  the  one 
passes  to  the  free  surface  of  the  hippocampus  and  constitutes  the  alveus,  the  other  passes 
to  the  lateral  wall   and   roof  of  the  inferior  horn   of  the   lateral  ventricle.      The  alveus  is 


Layer  of. 
poly7norphk  cells 


pyramidal  cells 


Molecular  layer 

Fig.   117. — Hippocampus 


nd  gyrus  dentatus  in  transverse  section.     Schematic. 


THE    HIPPOCAMPUS.  121 

continuous  with  the  fimbria.  The  uppermost  layer  of  the  gray  substance,  the  substmitia 
reticularis  alba,  corresponding  to  the  molecular  layer  of  the  typical  cortex,  divides  into 
a  superficial  and  a  deep  stratum.  The  superficial  layer  adjoins  the  molecular  layer  of  the 
gyrus  dentatus  and  forms  the  lamina  medtcllaris  circiimvolula.  The  deep  layer  forms  the 
stratum  laainosiim ,  that  arches  around  and  embraces  the  lamina  medullaris  and  ends  in  a 
recurved  hook  at  the  medial  side  of  the  cell-layer  of  the  gyrus  dentatus.  Between  the 
lamina  medullaris  circumvoluta  and  the  stratum  lacunosum,  lies  the  stratum  violeculare. 
The  pyramidal  cells  of  the  subinculum  gradually  collect  into  a  single  layer  of  cells  as  they 
approach  the  hippocampus.  At  first  the  arrangement  of  the  cells  is  still  irregular,  towards 
the  gyrus  dentatus  the  cells  form  a  single  thick  layer,  but  within  the  terminal  sheet  of 
the  hippocampus  they  once  more  are  irregularly  disposed.  In  this  way  two  special  zones 
are  produced,  a  deep  layer  of  pyramidal  cells,  the  stratum  lucidum,  and,  between  the 
latter  and  the  stratum  lacunosum,  the  stratum  radiatum,  so  called  on  account  of  the 
traversing  long  primordial  stems  of  the  pyramidal  cells.  The  layer  of  polymorphic  cells 
is  known  as  the  stratum  oriens.  The  gyrus  dentatus  exhibits  three  strata  :  the  molec- 
ular layer,  the  granule-layer  or  the  stratum  granulosum,  and  the  layer  of  polymorphic 
cells.  The  relations  between  the  strata  of  the  modified  cortex  of  the  special  convolutions 
and  those  of  the  typical  cerebral  cortex  are  shown  in  the   following   table  and  Fig.    117: 

Cerebral  Cortex  Hippocampus  Gyrus  dentatus 

{Lamina  medullaris  circumvoluta  \ 
Stratum  moleculare  \  Molecular  layer 

Stratum  lacunosum  ) 

,  -J  ,      „      f  ■Stratum  radiatum  \  Granule-layer    or    stratum 

Layer  of  pyramidal  cells  -^  ^^^.^^^^^^^  ^^^^.^^^^^^  |  granulosum 

Layer  of  polymorphic     \   ^,     ,  ■  \  Layer  of  polymorphic  cells 

cells.  \  ^^'''''""'  '"''^'"  \         or  stratum  oriens 

White  substance  I  Alveus 

HIPPOCAMPUS. 
The  individual  layers  exhibit  the  following  cells: 

1.  Lamina  medullaris  and  stratum  moleculare: 

a.  Small  cells  of  Golgi  II  type. 

b.  Fusiform  cells,   with  nerve-processes  that  break  up  in  stratum  moleculare. 

2.  Stratum  lacimosum  : 

Small    triangular    or    stellate  cells,    with    ascending    and    descending    dendrites    and 
nerve-processes  that  split  up  in  the  stratum  lacunosum. 

3.  Stratum  radiatum: 

a.  Cells    of    the    same    character    as    those    of    the    stratum    lacunosum — aberrant 

cells  of  the  stratum  lacunosum. 

b.  Pyramidal  cells — aberrant  cells  of  the  stratum  lucidum. 

c.  Cells  of  Golgi  11  type. 

d.  Triangular   or   fusiform    cells,    descending    nerve-processes   ending   around    the 

pyramidal  cells. 


122  THE   FIBRE-TRACTS. 

4.  Stratum  liicidiim: 

Pyramidal  cells,  with  long  primordial  stems  ascending  within  the  stratum  radiatum 
and  nerve-processes  running  to  the  alveus.  Within  the  portion  of  the  hippo- 
campus bordering  the  gyrus  dentatus,  giant  pyramidal  cells  are  found. 
Each  of  the  nerve-processes  of  these  elements  gives  off,  soon  after  its  origin 
from  the  cell,  a  collateral,  which  traverses  the  stratum  radiatum  and  passes 
to   the  stratum  lacunosum. 

5.  Stratum  oriens: 

a.  Aberrant  pyramidal  cells. 

b.  Cells  with  ascending  nerve-processes,   that  end  around  the  pyramidal  cells. 

c.  Martinotti  cells. 

Along  with  the  fibres  passing  from  the  cortex  to  the  alveus,  are  found  also  those 
which  come  from  the  alveus  and  end  within  the  cortex. 

GYRUS   DENTATUS. 

The  gyrus  dentatus  constitutes  a  small  modified  cerebral  cortex,  which  adjoins  the 
lamina  medullaris  circumvoluta  of  the  hippocampus  and  receives  within  its  hilus  the  end 
of  the  hippocampus.  The  white  substance  of  the  gyrus  dentatus  is  net  directly  apphed 
to  the  layer  of  polymorphic  cells,  but  is  separated  from  the  latter  by  the  cortical  forma- 
tion, which  corresponds  to  the  region  of  the  hippocampus  bordering  the  gyrus  dentatus. 
It  follows,  that  the  fibres  coming  from  the  gyrus  dentatus  break  through  the  end  of  the 
hippocampus  lying  within  the  hilus,  the  alveus,  therefore,  representing  the  cortical  white 
substance  of  both  the  hippocampus  and  the  gyrus  dentatus. 

Passing  from   the   tissura  hippocampi   towards  the  ventricle,  the  following  strata  are 

encountered  : 

a.    Molecular  layer,  bordering  the  lamina   1 

medullaris  of  the  hippocampus,  t 

I     c-i     1  7  \  Gyrus  dentatus. 

0.    Citratum  gramdosum,  1      ■' 

c.  Layer  of  poly77iorphic  cells,  j 

d.  Molecular  layer,  1 

e.  Layer  of  giant  pyramidal  cells,    1    ^^. 

r     T  r       ,  1  ■        ,,  I"   Hippocampus. 

/.   Layer  of  polymorphic  cells, 

g.   Alveiis. 
The  cells  exhibited  by  the  individual  strata  of  the  gyrus  dentatus  are  the  following: 

1.  Molecular  layer: 

a.  Cells  of  Golgi  II  type, 

b.  Aberrant  granule-cells. 

2.  Sti'atum  grannlosum. 

This  layer  is  formed  of  the  granule-cells,  closely  placed  and  disposed  in  several 
rows.  The  cells  are  modified  pyramidal  cells,  distinguished  by  the  absence  of  the  basal 
dendrites  and  a  primordial  stem.  The  ascending  dendrites  end  within  the  molecular 
layer,  while  the  nerve-process  passes  through  the  layer  of  polymorphic  cells,  then 
through  the  molecular  layer  and  the  stratum  of  pyramidal  cells  of  the  hippocampus,  and 
exhibits    during    its  further  course  peculiar  local  thickenings,    with    small  protruding    out- 


CEREBRAL   LOCALIZATION.  123 

growths.  The  nerve-processes  unite  into  a  bundle  and  then  end,  after  forming  a 
reticular  plexus,  around  the  cell-bodies  of  the  large  pyramidal  cells  and  their  dendrites. 
They  establish  relations,  therefore,  between  the  granule-cells  and  the  giant  pyramidal 
cells  of  the  hippocampus,  from  which,  in  turn,  the  impulse  may  be  conveyed  to  other 
pyramidal  cells  by  the  collaterals  that  pass  to  the  stratum  lacunosum. 

3.    Layer  of  polymorphic  cells: 

a.  Cells  with  ascending  nerve-processes,   ending  within  the  granule-layer, 

b.  Cells  with  ascending  nerve-processes,   passing  to  the  alveus, 

c.  Cells  of   Golgi  II  type. 

As  in  the  hippocampus,  so  here,  among  the  fibres  passing  from  the  gyrus  dentatus 
are  those  coming  from  the  alveus  and  ending  within  the  gyrus  dentatus. 

In  its  further  course,  the  gyrus  dentatus  continues,  as  the  induseum  griseum,  over  the 
corpus  callosum.  The  medial  and  lateral  thickenings,  the  stria  Lancisii  and  the  taenia  tecta, 
likewise  display  the  character  of  cortex  ;  within  the  stria  Lancisii  a  molecular  layer  with 
tangential  fibres,   a  middle  layer  with  fusiform  cells  and  a  deep  layer  are  distinguishable. 

CEREBRAL  LOCALIZATION. 

The  various  subdivisions  of  the  brain  are  broadly  divided,  with  regard  to  their 
functions,  into  two  chief  groups,  the  higher  and  the  lower.  The  higher  subdivisions  are 
the  cerebral  hemispheres,  and  in  these  the  cerebral  cortex,  which  through  the  great 
de\-elopment  of  the  cerebral  mantle  and  the  formation  of  the  convolutions  attains  such 
extraordinary  expansion,  plays  the  principal  role  and  represents  the  material  substratum 
of  intellectual  activity.  The  lower  subdivisions  are  interposed  between  the  cerebral 
hemispheres  and  the  spinal  cord  and  include  the  medulla  oblongata,  the  pons,  the  cere- 
bellum, the  region  of  the  corpora  quadrigemina,  and  the  cerebral  ganglia— that  region, 
therefore,  also  designated  as  brain-stem.  These  lower  parts  possess  no  direct  import  for 
intellectual  activity,  but  have  rather  the  task  of  regulating,  independently  of  conscious- 
ness or  volition,  the  many  functions  necessary  for  the  maintenance  of  the  body.  "The 
lower  brain  segments  supply  an  apparatus,  by  which  the  general  condition  of  the  body 
may  be  reflected  from  within.  For  the  moulding  of  the  intellectual  processes,  the 
mechanism  of  the  cerebrum  proper  is  authoritative." — (Flechsig. ) 

It  is  unquestionably  the  service  of  the  anatomist,  Franz  Joseph  Gall,  first  to  have 
recognized  the  significance  of  the  cerebral  cortex  for  intellectual  activity.  Since  Gall, 
anatomists  have  ceased  to  seek  a  definite  point  in  the  brain,  to  which  all  motor  and 
sensory  ner%-es  converge  and  which  might  be  identified  anatomically  as  the  seat  of  the 
centralized  soul.  As  well  known,  Ren6  Descartes  interpreted  the  pineal  body  as  the 
organ  of  the  soul  ;  Sommering  located  the  sensorium  commune  in  the  fluid  of  the  ven- 
tricles ;  according  to  Varolius,  the  soul  had  its  seat  in  the  soft  brain-substance ;  Thomas 
Willis  regarded  the  central  ganglia  as  perception-centres,  and  the  corpus  callosum  as  the 
seat  of  the  imagination,  while  he  placed  thought  within  the  cerebral  convolutions.  Gall, 
moreover,  established  the  principle,  that  the  individual  convolutions  are  not  all  intellec- 
tually equivalent  and  in  this  fundamental  view  already  approached  the  modern  theory  of 
localization.  In  setting  up  his  own  localization  theory  he  went  too  far,  in  that  he  sub- 
dividcfl  the  entire  cerebral  surface  into  twenty-seven  separate  areas,  which  areas  were  the 


124  THE   FIBRE-TRACTS. 

carriers  of  definite  intellectual  faculties  and,  further,  that  along  with  the  greater  develop- 
ment of  such  a  definite  brain-area,  a  corresponding  stronger  projection  appeared  on  the 
skull.  Following  the  theory,  the  possibility  was  assumed,  that,  by  careful  examination 
of  the  skull,  a  person's  endowment  or  character  might  be  determined.  In  the  scientific 
world,  Gall's  phrenology  did  not  long  endure.  Although  the  present  theory  of  localiza- 
tion differs  entirely  in  its  essentials  from  phrenology,  we  must  nevertheless  admit  that 
localization  was  advanced  more  by  Gall  than  by  the  labors  and  views  of  the  physiologist, 
Flourens,  who  defended  the  theory  of  the  equivalence  of  the  parts  of  the  cerebrum. 
Gall  and  his  pupil,  Bouillaud  (1825),  had  already  learned  that  circumscribed  injury  of 
the. cerebrum  in  the  frontal  region  may  lead  to  disturbances  of  speech. 

According  to  Gall  and  Bouillaud,  in  1836  the  French  physician,  Marc  Da.x,  furnished 
the  proof,  that  motor  aphasia  appeared  only  after  disease  of  the  left  cerebral  hemisphere, 
and  in  1861  Broca  announced  the  theorem,  that  particularly  the  left  third  frontal  convo- 
lution was  the  seat  of  speech  ;  hence  this  region  is  even  to-day  commonly  called  Broca' s 
convolution. 

This  discovery  of  the  motor  speech-centre  by  Broca  was  the  foundation  of  the  theory 
of  localization.  Although  the  proof  of  the  functional  variation  of  the  cerebral  cortex 
shattered  Flourens'.  teaching  of  functional  equivalence,  this  "theory  was  finally  entirely 
overthrown,  not  only  by  further  pathological  experience,  but  especially  by  experimental 
physiology,  since  in  1870  Fritsch  and  Witzig  discovered  the  electrical  irritability  of  the 
cerebral  cortex.  These  investigators  succeeded  in  inducing  movements  of  certain  parts  of 
the  body  by  stimulation  of  definite  cortical  regions  by  means  of  the  galvanic  current,  and, 
further,  reached  the  conclusion,  that  while  stimulation  of  certain  cortical  regions  produced 
movements,  no  such  result  followed  stimulation  of  other  regions.  These  investigations 
were,  confirmed  and  supplemented  in  1873  by  those  of  Ferrier,  who  employed  the 
faradic  current  instead  of  the  galvanic.  In  consequence  of  these  observations,  it  was 
possible  to  establish  a  definite  cortical  region  as  the  centre  for  movement.  Other  investi- 
gators, particularly  Nothnagel,  Carville  and  Duret,  Goltz  and  Munk,  subsequently 
succeeded,  reversing  the  order,  in  producing  paralysis  of  certain  muscles  and  impairment 
of  certain  sensory  activities  by  removal  or  destruction  of  definite  cortical  regions.  These 
labors,  along  with  the  numerous  investigations  of  other  workers,  have  established  with 
increasing  stability  the  localization  of  the  functions  of  the  cerebral  cortex. 

It  is  admitted,  therefore,  that  the  individual  regions  of  the  cerebral  surface  are  not 
equivalent,  but  of  entirely  different  significance.  Each  cortical  field  presiding  over  a 
definite  function  is  designated  as  a  centre,  and  of  such  cerebral  cortical  centres,  although 
as  yet  not  accurately  delimited,  we  recognize  the  following. 

THE    MOTOR    CENTRE. 

According  to  the  newer  investigations,  the  motor  centre  embraces  especially  the 
anterior  central  or  precentral  convolution,  and,  further,  the  posterior  part  of  the  frontal 
lobe  and  the  lobulus  paracentralis.      It  includes  the  following  regions. 

a.  Upper  region  :  lobulus  paracentralis  and  the  upper  quarter  of  the  precentral 
convolution — the  centre  for  the  movements  of  the  lower  extremity.  A  further  separation 
into  particular  centres  for  certain  groups  of  muscles  is  often  made  ;  the  data,  however, 
are  so  far  from  accord,   that  a  subdivision  into  definite   subcentres  may  be   here  omitted. 


CEREBRAL    LOCALIZATION. 


125 


Motor  centre 


The  largest  part  of  the  superior  frontal  convolution,  especially  the  region  bordering  the 
paracentral  lobule  and  the  upper  fourth  of  the  precentral  convolution,-  constitutes  the 
centre  for  the  muscles  of  the  trunk. 

b.  Middle  region:  the  middle  two-fourths  of  the  precentral  convolution — the 
centre  for  the  movements  of  the  upper  extremity.  The  further  delimitation  within  this 
centre  of  subcentres    for    movements  of   the 

fingers,  the  hand,  the  arms  and  the  shoulder, 
is  so  ordered,  that  the  centre  for  the  fingers 
occupies  the  lowest  position,  and  that  for 
the  shoulder  the  highest. 

c.  Lower  region  :  the  lower  fourth 
of  the  precentral  con\olutipn — the  centre  for 
the  musculature  of  the  face,  the  tongue, 
mastication,  the  laryn.\  and  the  pharyn.x. 
Small  special  centres  for  the  upper  and 
lower  facial  nerve  are  assumed  to  exist. 

Within  the  posterior  part  of  the  middle 
frontal  convolution  lies  the  centre  for  the 
movements  of  the  eyes  and  of  the  head, 
particularly  for  the  direction  of  the  head  and 

the  eyes  towards  the  opposite  side  (conjugate  deviation).  According  to  other  investi- 
gators, a  second  projection  centre  for  the  winking  movements  of  both  eyes  has  its  seat 
in  the  g>'rus  angularis. 


118. —  Cerebral    localizatu 


Pig.  119. — Cerebral  localization.     The  chief  regions  of  the  motor  centre. 


In  regard  to  the  motor  centres  it  is  particularly  to  be  noted,  that  stimulation  within  the 
centre  calls  forth  contraction  and  movements  of  the  corresponding  muscle-area  of  the  opposite 
half  of  the  body,  and  that  in  like  manner  injuries  lead  to  paralysis  in  the  opposite  side  of  the 
body.  This  will  be  further  discussed  in  connection  with  the  motor  conducting  paths  (page  139). 


126 


THE   FIBRE-TRACTS. 


This  rule  is  not,  however,  without  exception.  From  certain  centres,  not  only  the 
corresponding  muscles  of  the  opposite  side  are  controlled,  but  also  those  of  the  same 
side;  that  is,  there  exists  for  certain  muscles  a  bilateral  innervation.  This  is  true  for 
those  muscles  whose  action,  as  a  rule,  is  not  unilateral  but  symmetrically  bilateral,  as,  for 
example,  in  the  case  of  the  frontalis,  orbicularis  oculi  and  corrugator  supercilii  muscles 
supplied  by  the  upper  facial  branch,  or  the  muscles  of  mastication,  of  the  pharynx  and 
of  the  larynx.  This  bilateral  innervation  explains  the  fact,  that  after  unilateral  destruction 
of  such  centres  the  paresis  of  the  muscles  concerned  is  not  pronounced,  since  the 
necessary  stimulus  may  still  be  supplied  from  the  unaffected  centres  of  the  opposite 
hemisphere. 

THE   SENSORY    CENTRES. 

a.  The  sensory  area,  including  the  centres  for  touch,  pain  and  temperate  sensi- 
bility, embraces  especially  the  postcentral  convolution  and  the  adjoining  anterior  part  of 
the  parietal  lobe  and,  perhaps,  even  extends  onto  the  precentral  convolution.  The 
position-  and  movement-sensibility,  as  well  as  space-  and  orientation-sense,  are  trans- 
ferred to  this  same  region.  The  impulses,  passing  to  the  sensory  area,  come  essentially 
from  the  opposite  half  of  the  body. 

b.  The  auditory  centre  is  located  in  the  middle  part  of  the  gyrus  temporalis 
superior  and  includes  additionally  the  gyri    transversi  of  the  upper  temporal  convolution, 

that    lie    buried    within    the 
Motor  centre  fissurc  Cerebri  lateralis. 

c.  The  visual  centre 
lies  within  the  cuneus,  par- 
ticularly within  the  cortex  of 
the  fissura  calcarina,  perhaps 
extending  onto  the  gyrus 
lingualis. 

d.  The  olfactory  cen- 
tre is  situated  within  the 
anterior  part  of  the  gyrus 
hippocampi  and  the  hippo- 
campus. 

e.  The  gustatory  cen- 
tre has  as  yet  not  been  definitely  located,   but  probably  adjoins  that  for  smell. 

The  motor  centres  and  the  individual  sensory  regions  or  sense-centres  are 
designated  also  as  projection  centres,  for  the  reason  that  the  impulses  passing 
from  the  stimulus-receiving  organs  (skin,  muscles,  joints  and  the  higher  sense- 
organs),  and  conveyed  by  the  sensory  nerves  of  the  central  nervous  system, 
are  radiated  or  projected,  as  it  were,  to  the  sense-centres,  while  the  impulses  from 
the  motor  centres  are  similarly  projected  towards  the  periphery  and  conveyed  by  the 
motor  nerves  especially  to  the  muscles.  Stimulation  within  the  sense-centres  induces 
sensation  (touch,  sight,  hearing,  smell,  etc.)  ;  stimulation  within  the  motor  zone 
leads  to  movements.  These  incoming  and  outgoing  conductions  follow  quite  definite 
paths,  which  are  termed  afferent  or  centripetal  and  efferent  or  centrifugal  projection- 
tracts  respectively. 


,  Visual 
centre 


Fig.  120. — Cerebral  localization.     Visual  and  olfactory  centres. 


ASSOCIATION    CENTRES.  127 

Viewing  the  surface  of  the  cerebral  hemispheres  and  imagining  the  individual  pro- 
jection centres  outlined,  it  will  be  evident  that  the  latter  occupy  only  a  certain  part, 
perhaps  a  third,  of  the  entire  cerebral  cortex.  In  addition  to  these  motor  and  sensory 
fields,  there  remains  a  large  area  that  embraces  certain  parts  of  the  frontal,  parietal, 
occipital  and  temporal  lobes,  together  with  the  deeply  situated  central  lobe  or  the 
insula — a  tract  of  still  slightly  known  function.  According  to  Flechsig,  this  entire  large 
area  is  designated  the  association  centres,  of  which,  following  him,  an  anterior,  a  middle 
and  a  posterior  association  centre  are  distinguished.  The  anterior  or  frontal  centre  in- 
cludes the  fore-part  of  the  frontal  lobe;  the  middle  or  insular  centre,  the  island  of  Reil; 
and  the  posterior  or  parieto-occipito-temporal  centre,  a  large  part  of  the  occipital  and 
temporal  lobes  and  almost  the  entire  parietal   lobe. 

According  to  the  theory  advanced  first  by  Flechsig,  these  association  areas 
constitute  the  substratum  for  the  higher  psychic  functions — an  apparatus  which  collects 
the  activities  of  the  sense-centres  to  higher  unity,  and  comprises  centres  of  all  the  more 
comple.x  associations.  They  are  the  chief  bearers  of  what  we  call  experience,  knowledge 
and  cognizance  and,  in  part,  of  speech,  in  short  the  intellectual  centres  proper.  Flechsig 
was  led  to  the  advancement  of  this  theory  chiefly  through  his  histological  investigations 
based  on  the  method  of  the  development  of  the  medullary  sheath.  He  proved  that  the 
myelin-ripening  of  the  individual  nerve-tracts  proceeds  from  below  upward,  that  is  from 
the  spinal  cord  and  the  lower  brain-segments  towards  the  cortex  of  the  end-brain. 
Already  at  birth,  according  to  Flechsig,  the  individual  tracts  have  reached,  in  large 
part,  their  development  within  the  lower  divisions  of  the  brain,  while  within  the  cerebrum 
only  few  paths  of  conduction  have  developed.  At  first,  one  sense-conductor  after  the 
other  gradually  pushes  out  towards  the  cerebral  cortex.  In  the  new-born  child,  only 
two  of  the  sense-centres,  the  olfactory  and  gustatory,  are  developed ;  then  follow  the 
centres  for  tactile  sense,  for  sight  and,  lastly,  for  hearing.  Only  subsequent  to  the  com- 
pleted development  of  the  sense-centres,  does  the  development  of  the  intellectual  centres 
begin  within  the  individual  territories.  Medullary  fibres  proceed  from  the  projection 
centres  to  the  neighboring  association  areas,  the  latter  likewise  become  functionally  active 
and  eventually  numerous  tracts  bind  both  kinds  of  centres  with  each  other.  Based  on 
further  investigations,  Flechsig  later  subdivided  the  entire  cerebral  cortex  into  thirty-six 
different  areas,  according  to  the  time  of  completed  myelination.  The  areas  first  be- 
coming medullated  correspond  to  the  projection  centres ;  then  follow  the  embryonic 
intermediate  centres  and,  finally,  the  terminal  districts,  which  exclusively  form  the 
association  centres. 

According  to  Flechsig,  the  projection  centres  differ  also  anatomically  from  the 
association  ones,  since  only  the  former  are  connected  by  centripetal  and  centrifugal  pro- 
jection tracts  with  the  lower  brain-centres,  while  within  the  association  centres  such  projec- 
tion tracts  are  altogether  wanting.  The  association  areas  are  connected  by  fibre-tracts 
only  with  the  projection  centres,  from  which  they  receive  sensory  stimuli ;  on  the  other 
hand,  they  may  influence  the  sensory  areas  by  reflex  stimuli  or  inhibition.  The  associa- 
tion and  projection  centres  also  vary  in  their  histological  make-up,  since  the  association 
centres  exhibit  a  specific  although  uniform  texture,  while  the  projection  centres  present  a 
structure  which  not  only  differs  from  that  of  the  association  centres,  but  varies  within  the 
individual  fields. 


128  THE    FIBRE-TRACTS. 

This  important  theory  of  Flechsig,  however,  can  no  longer  be  accepted  in  its 
entirety.  Further  investigations  have  not  substantiated  the  assumption,  that  only  a  por- 
tion of  the  cortex  is  connected  with  the  lower  lying  brain-centres  by  means  of  projection 
tracts,  since  such  paths  have  been  proven  also  for  the  association  fields  mapped  out  by 
Flechsig.  Furthermore,  it  has  been  determined,  that  not  only  the  projection  centres  possess 
a  special  and  for  each  region  specific  texture,  but  that  there  also  exists  within  the  asso- 
ciation tract  a  large  number  of  areas  of  different  structure.  As  has  been  shown  by  the 
investigations  of  Vogt  and  Brodmann,  the  entire  cerebral  cortex  may  be  mapped  out  in 
numerous  fields,  which  differ  from  one  another  in  regard  to  cellular  stratification,  as  well 
as  in  regard  to  fibre-relation,  there  existing  a  cyto-  and  a  myelo-architectonic  differentia- 
tion of  the  cerebral  cortex  (Figs.  114  and  115). 

Concerning  the  relations  of  each  individual  anatomically  definable  field  to  function, 
however,  we  still  know  very  little,  and  it  remains  for  future  physiological  and  clinico- 
pathological  investigations  to  advance  our  understanding  concerning  this  problem.  With 
Brodmann  we  may  assume,  "that  each  specific  cytological  difference  must  be  the  expres- 
sion of  a  definite  physiological  dignity  and  that,  therefore,  all  the  variously  structured 
cortical  fields  also  preside  over  different  functions.  Not,  of  course,  in  the  sense  that  one 
assigns  complex  intellectual  processes  or  attributes  to  specially  delimited  territories,  but  in 
the  only  warranted  sense  of  Wernicke,  who  associates  only  the  most  elementary  functions 
with  definite  localities  of  the  cerebral  cortex."  A  question,  for  which  the  answer  has  long 
been  sought,  is  the  existence  of  definite  recollection  or  memory  centres.  Many  facts 
point  to  the  actual  existence  of  such  memory  centres  beside  the  projection  centres.  Thus, 
clinical  cases  are  known,  in  which  loss  of  a  perception  region  was  attended  with  cessation 
of  the  corresponding  perception,  but  not  of  the  related  memory-pictures  ;  on  the  contrary, 
certain  cases  with  cortical  lesions  in  the  immediate  vicinity  of  the  perception  centres,  for 
example,  of  the  convolutions  adjoining  the  visual  and  auditory  centres,  exhibited  neither 
blindness  nor  deafness,  but  failure  of  memory  and  disturbances  of  the  function  of  recog- 
nition. Thus  lesions  of  both  occipital  lobes  lead  to  so-called  visual  agnosia  or  perception 
blindness.  The  patient  may  still  be  able  to  give  information  regarding  the  form  and 
color  of  an  object,  but  the  object  itself  is  unknown,  he  being  no  longer  able  to  recog- 
nize the  object  or,  usually,  its  spatial  relations.  Further,  lesions  of  the  left  temporal  lobe 
cause  the  so-called  auditory  agnosia  or  perception  deafness,  in  which  condition  not  only 
the  spoken  words,  but  also  auditory  stimuli  of  all  kinds  are  no  longer  understood. 
Likewise,  lesions  situated  in  the  middle  third  of  the  postcentral  convolution,  or  farther 
backward  in  the  parietal  lobe,  may  lead  to  so-called  tactile  agnosia,  in  which,  for 
example,  the  form  of  any  object  no  longer  is  recognized,  notwithstanding  the  integrity 
of  the  individual  impressions  necessary  for  touch-,   space-  and  muscle-sense. 

THE   SPEECH    CENTRES. 

The  speech  centre  in  its  entirety  includes  certain  cortical  areas  of  the  lateral  surface 
of  the  hemisphere  and,   in  right-handed  individuals,   is  located  on  the  left  side. 

a.  The  motor  speech  centre,  Broca's  centre  presiding  over  the  ability  to  speak, 
lies  within  Broca's  convolution  embracing  the  base  of  the  gyrus  frontalis  inferior.  It 
extends,  perhaps,  also  to  the  adjacent  part  of  the  lowest  region  of  the  precentral  convo- 
lution and  to  the  anterior  part  of  the  insula.      Upon  the  integrity  of  this  centre  depends 


THE   SPEECH    CENTRES. 


129 


-Cerebral  localizatit 


the  ability  to  carry  out  the  co-ordinated  movements  necessary  in  speaking.  Damage  of 
the  centre  leads,  therefore,  to  abolition  of  the  execution  of  motor  speech.  Voluntary 
speech,  repeating  words  or  reading  aloud  are  no  longer  possible.  This  centre,  therefore, 
is  also  termed  the  centre  of  motor  aphasia. 

b.  The  sensory  speech  centre,  the  tone-picture  or  auditory  centre,  lies  within 
the  posterior  third  of  the  gyrus  temporalis  superior  and  the  adjoining  part  of  the  gyrus 
supramarginalis.  It  is  also  known  as  Wernicke  s  centre  and  represents  the  cortical  region 
where  the  memory-pictures  of  the  heard  and  spoken  words  are  retained.  If  the  centre 
be  injured,  the  patient,  while 

still        hearing       the       spoken  Auditory  centre  —   Wernicke 

word,  can  no  longer  compre- 
hend what  he  hears.  He  has 
lost  speech-understanding. 
The  centre  is  also  designated 
as  the  centre  for  word-deaf- 
ness or  sensory  aphasia. 

c.  The  visual  cen- 
tre, where  the  memory-pic- 
tures of  written  characters 
are  stored,  lies  within  the 
gyrus  angularis.     Injury  of 

the  centre  is  followed  by  inability  to  recognize  the  printed  or  written  letters,  or  to  form 
words  from  them.     The  centre  is  also  termed  the  centre  for  word-blindness  or  alexia. 

d.  A  special  writing  centre  is  still  often  assumed  to  lie  within  the  base  of  the  gyrus 
frontalis  medius.  Its  existence,  however,  is  scarcely  longer  to  be  accepted,  since  the 
centre  for  writing  is-  blended  with  the  motor  centre  for  the  hand  within  the  middle  region 
of  the  precentral  convolution. 

These  speech  centres  are,  therefore,  centres  of  memory,  namely,  for  the  movement- 
conceptions  of  articulation,  the  acoustic  pictures  of  speech  and  the  visual  pictures  of 
written  speech.  Individuals,  who,  in  consequence  of  lesions  of  these  centres,  have  lost 
the  memory  of  the  motor,  auditory  and  visual  conceptions  of  speech,  are  neither  paralyzed, 
deaf,  nor  blind,  but  only  wanting  in  speech-understanding.  We  are,  therefore,  warranted 
in  assuming  the  existence  of  memory  centres  beside  the  projection  centres  ;  further,  it 
must  be  noted,  that  the  projection  centres  serve  not  only  sensation  and  innervation,  but 
also  memory,  and,  on  the  other  hand,  that  the  regions  adjoining  the  projection  centres 
are  not  to  be  regarded  as  exclusive  commemorative  centres,  since  the  existence  of 
projection  tracts  to  them  has  been  proven. 

Concerning  the  association  function  of  the  cerebrum,  we  must  assume  that  the 
binding  together  of  conceptions  or  recollections  of  the  same  kind  occurs  in  the  cortex 
within  the  individual  cortical  fields,  but  that  all  the  higher  association  processes  are  con- 
nected with  the  collective  activity  of  many,  perhaps  of  all,  the  cortical  regions. 

Finally,  it  must  be  especially  emphasized,  that  the  two  cerebral  hemispheres  are 
functionally  by  no  means  identical.  In  connection  with  localization  of  the  speech  centre, 
it  has  been  pointed  out,  that  in  right-handed  individuals  the  left  hemisphere  is  concerned. 
Not  only  for  speech   does  the  left   hemisphere   outweigh  the  right,  but  also  for   manipu- 

9 


I30 


THE   FIBRE-TRACTS. 


lation.  For  proof  of  this  we  are  indebted  especially  to  the  investigations  of  Liepmann, 
who  has  made  us  acquainted  with  the  clinical  picture  of  apraxia.  By  apraxia  is  under- 
stood the  inability  to  execute  the  appropriate  movements  during  continued  motion  ;  that 
is,  the  apraxic  patient  is  still  able  to  carry  out  certain  simple  movements,  as  flexing,  lower- 
ing, raising  or  extending  the  arm,  but  has  lost  the  ability  to  perform  com.binations  of 
consecutive  movements,  such  as  made  in  greeting,  beckoning,  or  threatening.  Such 
expressive  movements  are  executed  in  an  entirely  abnormal  manner,  likewise  the  imitation 


paralys: 


I  the  right  side  and  dysprax 


lesions  in  b  and  c  cause  dyspraxia  on  the  left  side;  le 


impaired  combination-movement,  on  the  left; 
in  d  causes  paralysis  on  the  right  side. 


of  definite  movements,  and  objects  are  no  longer  properly  used  or  handled.  In  many 
lesions  of  the  left  hemisphere,  followed  by  paralysis  and  apraxia  of  the  right  hand,  a 
similar  affection  of  the  left  hand  may  be  recognized.  Moreover,  in  numerous  cases  of 
extensive  lesion  of  the  corpus  callosum,  dyspraxia  of  the  left  hand  is  present.  According 
to  Liepmann,  one  is,  therefore,  warranted  in  assuming  that  the  recollection  of  certain 
acquired  dexterities  and  also  the  supervision  of  the  execution  of  the  same  are  in  predom- 
inating degree  concerns  of  the  left  hemisphere,  which  are  conveyed  to  the  right 
hemisphere  by  means  of  the  corpus  callosum. 


PATHS    OF  CONDUCTION.  131 


GENERAL    DIVISION    OF   THE    CONDUCTION    PATHS. 

The  entire  nervous  system  is  built  up  of  nervous  units  or  neurones.  With  regard 
to  their  physiological  tasks,  the  neurones  may  be  divided  into  two  chief  groups,  those 
which  conduct  impulses  centrifugally  and  those  which  conduct  centripetally. 

The  centrifugal  paths  serve  to  convey  impulses  from  the  central  nervous  system  to 
peripheral  organs,  especially  to  the  organs  of  movements  or  the  muscles.  These  may, 
in  a  general  way,  also  be  called  ynotor  paths.  The  centripetal  paths,  on  the  contrary, 
convey  impulses  coming  from  the  periphery  to  the  central  nervous  system.  By  means 
of  them  we  receive  information  of  what  goes  on  in  nature  outside  of  our  bodies  (higher 
sense-nerves)  ;  they  bring  us,  however,  also  information  of  the  processes,  which  are 
taking  place  within  all  the  organs  of  our  own  bodies,  information  of  which  we  are  in 
part  conscious  and  in  part  unconscious,  the  latter  impulses  being  continually  active  in 
regulating  the  most  diverse  functions  of  our  bodies.  The  centripetal  paths  are  also,  in 
a  general  way,  designated  as  sensory  paths. 

It  is  particularly  to  be  noted,  that,  as  a  rule,  more  than  a  single  neurone  is  con- 
cerned in  the  constitution  of  the  afferent  and  efferent  paths,  and  that  these  are  made  up 
of  two,  three  or  several  neurones  in  sequence.  In  this  way,  for  example,  the  great 
cortico-muscular  paths,  by  means  of  which  voluntary  movements  of  the  musculature  of 
the  extremities  are  called  forth,  consist  of  two  neurones.  The  first  neurone  extends 
from  the  motor  cortical  centre  through  the  brain-stem  to  the  spinal  cord,  where  it  ends 
within  the  gray  substance  of  the  anterior  horn.  The  second  neurone  extends  from  the 
anterior  horn  of  the  cord  to  the  muscle.  In  like  manner,  the  sensory  path  is  composed 
of  several  neurones,  which  conduct  impulses  from  the  periphery,  as  for  example  the 
mtegument  of  the  leg,  through  the  peripheral  nerves,  the  spinal  cord  and  the  brain-stem 
to  the  sensory  region.  The  first  neurone  conducts  the  impulse  from  the  periphery  to  the 
spinal  cord  or  to  the  posterior  column  nuclei,  the  second  from  the  cord  or  the  nuclei  of 
the  posterior  column  to  the  thalamus,  and  the  third  neurone  arises  in  the  thalamus  and 
ends  in  the  cerebral  cortex.  Owing  to  the  insertion  of  further  neurones,  the  entire 
make-up  may  become  still  more  complicated,  in  this  manner  longer  or  indirect  paths 
being  formed  in  addition  to  the  shorter  direct  ones.  Since  the  motor  and  sensory  paths 
conduct  impulses  from  the  centre  to'  the  periphery  and,  conversely,  from  the  periphery 
to  the  centre,  that  is  similarly  "project,"   these  paths  are  also  called  projectio?i  tracts. 

Two  additional  important  connecting  links,  the  association  cojtdiiction  and  the  reflex 
conduction,  exist  between  the  motor  and  sensory  paths.  They  are  established  by  means 
of  intercentral  tracts.  Through  the  reflex  conduction,  a  reflex  movement,  the  reflex, 
is  liberated  without  the  accompaniment  of  psychic  processes.  This  conduction  is  effected 
by  the  .so-called  reflex  collaterals,  although  individual  neurones,  intercalated  between 
the  centripetal  and  centrifugal  tracts,  may  also  participate.  Let  us  take  as  an  example 
of  a  simple  reflex,  the  patellar  or  the  corneal  reflex.  The  patellar  reflex  is  manifested 
by  a  contraction  of  "the  quadriceps  muscle  and  extension  of  the  leg,  in  response  to 
stimulation  of  the  sensory  nerves  in  the  quadriceps  tendon,  as  when,  for  example,  the 
tendon  is  struck  with  the  percussion  hammer  below  the  patella,  while  the  leg  is  relaxed 
and  dependent.  This  entire  phenomenon  is  carried  out  by  the  following  paths :  the 
impulse  is  carried   from    the   tendon   of   the   muscle  to   the   spinal   cord,   by   way   of    the 


132 


^^^ 


Fig.   123. — Schematic  representation  of  the  physiologically  different  conductions.     Red,  centrifugal  tracts;  blue,  centripetal 
tracts;  black,  intercentral  tracts. 


PATHS   OF  CONDUCTION.  133 

spinal  ganglion,  by  the  sensory  or  afferent  nerves.  On  entering  the  spinal  cord,  the 
sensory  fibre  divides  into  an  ascending  and  a  descending  branch,  which  branches  subse- 
quendy  end  within  the  gray  substance  of  the  cord,  or,  as  in  the  case  of  the  ascending 
branch,  first  within  the  nuclei  of  the  posterior  column.  Before  dividing  into  these 
branches,  however,  the  entering  sensory  fibre  gives  off  a  delicate  collateral  branch,  a 
reflex  collateral,  which  runs  to  the  anterior  horn  and  there  ends.  Similar  reflex  collaterals, 
moreover,  are  also  given  off  from  the  ascending  primary  branch,  as  shown  in  Fig. 
123,  a.  B)-  means  of  these  reflex  collaterals,  the  impulse  may  be  directly  transferred  to 
motor  anterior  horn-cells  and  thence  conveyed  by  motor  fibres  to  the  muscle.  In  a 
similar  manner  the  corneal  reflex  or  tactile  lid-reflex  occurs.  This  reflex  consists  in  con- 
traction of  the  M.  orbicularis  oculi  on  touching  the  integument  of  the  eyelid,  the 
conjunctiva  or  the  cornea.  The  afferent  path  is  here  the  ophthalmic  branch  of  the  N. 
trigeminus.  From  the  sensory  trigeminal  fibres  entering  the  pons,  collateral  branches 
are  given  off,  which  pass  as  reflex  collaterals  to  the  nucleus  of  the  N.  facialis.  The 
efferent  path  lies  within  the  ocular  facial. 

In  place  of  the  reflex  collaterals,  however,  individual  neurones  may  transfer  the 
impulse  from  the  sensory  to  the  motor  tracts.  For  example,  a  sensory  fibre  on  entering 
the  spinal  cord  may  transfer  the  impulse  first  to  cells,  whose  axis-cylinders  do  not  leave 
the  cord,  as  do  those  of  the  motor  anterior  horn-cells  passing  to  the  periphery,  but 
enter  the  white  substance  and  divide  into  ascending  and  descending  branches.  These 
division-branches,  after  a  longer  or  shorter  course,  end  within  the  gray  substance  of 
cord-segments  of  higher  or  lower  levels  (Fig.  123,  b).  First  within  these  segments 
occurs  the  transference  to  true  motor  cells.  In  this  manner,  not  only  the  motor  cells 
of  the  same  level  are  impressed,  but  the  stimulus  is  carried  to  higher  and  lower  lying 
cord-segments  and,   consequently,   transferred  to  a  larger  number  of  motor  neurones. 

The  further  .possibility  exists,  that  the  impulse  may  be  conducted  from  the  spinal 
cord  by  the  ascending  tracts  to  the  higher  lying  subcortical  centres  and  that  first  here 
the  transference  to  the  motor  paths  occurs.  The  resulting  movements  are  mostly  more 
complicated  than  the  simple  reflexes,  although,  as  in  the  case  of  the  latter,  they  are 
unconsciously  executed.  As  shown  in  Fig.  123,  the  impulse  may  be  conducted  through 
certain  paths  from  the  spinal  cord  to  the  cerebellum,  thence  to  the  nucleus  ruber,  and 
from  the  latter  be  carried  downward  to  the  cord  and,   finally,   to  the  muscle. 

The  second  intercentral  connection  between  the  sensory  and  motor  parts  is  fur- 
nished by  association  conduction.  By  means  of  the  latter,  a  conscious  voluntary 
action  is  rendered  possible,  by  means  of  the  system  of  association  fibres  within  the 
cerebral  hemispheres.  An  impulse  is  carried  through  the  sensory  path  as  far  as  the 
cerebral  cortex  and  here  transferred  to  cells  within  a  certain  sense-centre ;  in  these  cells, 
it  may  be  assumed,  the  material  stimulus  is  released,  which  corresponds  to  psychic 
sensation.  One  may  simply  imagine,  that  from  this  locality  the  impulse  is  transferred 
by  an  additional  neurone  directly  to  the  cells  in  the  motor  cortical  region  and  thence 
farther  carried  by  the  motor  tract.  The  cortical  connection  is,  however,  far  more 
complex,  since  only  after  traversing  numerous  intermediate  neurones  does  the  impulse 
finally  reach  the  motor  centre  and  from  there  pass  to  the  motor  path,  since  cooperation 
of  the  various  cortical  centres  must  be  assumed  in  explanation  of  the  complex  psychic 
processes. 


134 


THE   FIBRE-TRACTS. 


CONDUCTION  PATHS  OF  THE  TELENCEPHALON. 

We  distinguish  two  chief  kinds  of  fibre  -  tracts,  association  tibres  and  projec- 
tion fibres. 

The  association  fibres  serve,  firstly,  to  bind  together  neighboring  or  remote 
regions  of  one  hemisphere  and,  as  such,  may  be  designated  as  the  association  fibres 
proper,  or  association  fibres  in  the  strict  sense.  Secondly,  they  serve  to  connect  the 
regions  of  both  hemispheres  and,   in  this  capacity,   are  termed  commissural  fibres. 

The  projection  fibres  unite  the  cortex  of  the  hemispheres  with  the  lower  lying 
parts  of  the  brain  and  with  the  spinal  cord — centrifugal  or  corticofugal  tracts ;  the  pro- 
jection fibres  also  include  those  passing  in  the  opposite  direction  from  the  lower  parts 
and  ending  within  the  cortex — centripetal  or  corticopetal  tracts. 

I.    ASSOCIATION   FIBRES. 

These  are  distinguished  as  short  and  long  fibres.  The  short  fibres  unite  adjoining 
convolutions  and  are  also  called  intralobular  or  U-fibres,  or  fibrae  propriae  or  arcuatae. 
The  long  fibres  connect  the  regions  of  one  hemisphere  which  are  more  or  less  separated 
and  are  also  termed  interlobar  bundles.       The  most  imoortant  of  these  are  : 


Fig.    124. — Association    fibr' 
projectioi 


nmissural     fibn 


Fig.  125. — Association  fibres.      Fasciculus  uncinatu 
fasciculus  longitudinalis  superior. 


-Association  fibres.      Cingulu 
longitudinalis  inferior. 


Fig.  127. — Association   fibres.      0.  F.,  fasciculus  occipito- 
frontalis;  V.,  fasciculus  uncinatus. 


PATHS   OF  CONDUCTION.  135 

a.  The  /asa'cu/us  uncinatus,  connecting  the  orbital  surface  of  the  frontal  lobe  with 
the  temporal  pole  and  the  anterior  part  of  the  gyri  temporales. 

b.  The  fasciculus  longitudinalis  superior  or  arcuatus,  connecting  the  operculum 
frontale  and  parietale  with  the  lobulus  parietalis  inferior,  the  occipital  lobe  and  the  pos- 
terior part  of  the  upper  and  middle  temporal  convolutions. 

c.  The  fasciculus  longitudinalis  inferior,  connecting  the  occipital  pole,  the  cuneus, 
the  gyrus  lingualis  and  fusiformis  with  the  temporal  pole. 

d.  The  citigulum,  also  called  the  fornix  periphericus,  running  within  the  gyrus 
fornicatus,  as  association  bundles  of  the  rhinencephalon. 

e.  The  fasciculus  fro7ito-occipilalis  (Forel-Onufrowicz),  running  immediately  beneath 
the  corpus  callosum,  over  the  nucleus  caudatus  and  within  the  corona  radiata,  and  con- 
necting the  frontal  with  the  occipital  lobe.  According  to  recent  investigations,  this 
bundle  is  to  be  regarded  rather  as  a  projection  fibre-system. 

/.   The  association   bundles,   which    pass    through   the   capsula    externa  and  extrema. 

II.    COMMISSURAL   FIBRES. 

These  unite  both  hemispheres  and  include  ; — 

a.  The  corpus  callosum,   connecting  the  cortical  districts  of  the  pallium. 

b.  The  comniissura  anterior,  connecting  the  districts  belonging  to  the  rhinen- 
cephalon. 

c.  The  comniissura  hippocampi,  connecting  the  same  districts  as  the  preceding. 
The  fibres    constituting   the  corpus   callosum    connect   the   cortical    districts    of   one 

hemisphere  with  those  of  the  other  hemisphere  and  form  the  radiatio  corporis  callosi, 
which  is  subdivided  into  a  pars  frontalis,  pars  parietalis,  pars  temporalis  and  pars  occip- 
italis (page  40).  The  comniissura  anterior  includes  a  pars  anterior  or  olfactoria  and  a 
pars  posterior  or  interhcmisphaerica.  The  pars  olfactoria  connects  the  lobus  olfactorius 
of  one  side  with  that  of  the  opposite  side.  The  pars  interhcmisphaerica  connects  the  two 
gyri  hippocampi  with  each  other  The  comniissura  hippocampi,  also  termed  the  fortiix 
transversus,  or  lyra  Davidis,  connects  the  two  hippocampi  with  each  other. 

III.   PROJECTION   FIBRES. 

These  unite  the  cortex  of  the  telencephalon  with  the  lower  lying  parts  of  the  brain, 
as  the  corpus  striatum,  thalamus,  regio  subthalamica,  corpora  quadrigemina,  pons  and 
medulla  oblongata,  and  with  the  spinal  cord.  They  arise  from  the  crest  of  the  convo- 
lutions and  form  collectively  the  corona  radiata.  To  them  also  belong,  as  already  noted, 
fibres  which  ascend  to  the  cortex  from  lower  parts  of  the  brain.  Short  and  long  tracts 
are  distinguished. 

A.  .Short   Tracts. 

I.  Fibres  passing  from  all  parts  of  the  cortex  to  the  thalamus  and,  vice  versa, 
from  the  thalainus  to  the  cortex — tractus  cortico-thalamici  and  thalamo- corticate s  or  the 
peduncles  of  the  thalamus.     Such  connections  include  : 

a.  The  cortex  of  the  frontal  lobe  with  the  anterior  end  of  the  thalamus ; 


136 


THE    FIBRE-TRACTS. 


b.  The    cortex    of    the    central  convolutions  and  of   the  anterior  part  of  the  parietal 
lobe  with  the  outer  and  inner  thalamic  nuclei ; 

c.  The    cortex    of    the    posterior    part  of  the  parietal  and  of  the  occipital  lobes  with 
the  puh'inar  ; 

d.  The    occipito-temporal    lobe    with    the  ventral  and  medial   parts  of  the  thalamus. 
An   important   ascending    tract    from   the   thalamus  to   the   cortex    is   the   tegmental 

tract,  or  tegmental  radiation.  The  fibres  pass  from  the  ventral  region  of  the  thala- 
mus, partly  through  the  in- 
ternal capsule  direct  to  the 
cortex  and  partly  first  through 
the  lenticular  nucleus,  sub- 
sequently joining  the  fibres 
following  the  internal  capsule. 
The  course  of  those  trav- 
ersing the  lenticular  nucleus 
is  shown  in  Fig.  129;  com- 
pare also  Fig.  154.  Fibres 
pass  also  in  the  opposite 
direction,  from  the  cortex 
to     the     ventral    part    of    the 

thalamus.  The  tegmental  path  is  also  designated  as  the  tractus  cortico-tegmentalis. 
2.  Fibres  passing  from  the  cortex  of  the  visual  centre  to  the  superior  colliculus 
and  to  the  corpus  geniculatum  laterale  and,  in  the  opposite  direction,  from  the  lateral  gen- 
culate  body  to  the  cortex.  The  corpus  geniculatum  laterale  and  the  pulvinar,  together 
with  the  superior  colliculus,  constitute  the  primary  visual  centre,  the  connection  of  these 
parts  with  the  cortical  visual  centre  within  the  occipital  lobe  forming  the  optic  radiation 
of  Gratiolet.     In  this  connection  it  is  to  be  noted,  that  the  fibres  to  the  cortex  pass  only 


— Projectif 
nd  poster! 


I  tracts.     Stalks  of  the  thalamus.      Fibre; 
r  corpora  quadrigemina  and  to  the  nucle 


to  the  anterior 
LS  ruber. 


Nucleus  ruber 


Ansa  fiedjiTtciilaris 


Corpora  gwadrigt 


Fig.  129. — Short  projection  tracts.  Fibres  to  thalamus,  to  nucleus  ruber  and  to  the  corpora  quadrigemina.  Fibres 
of  the  tegmental  tract,  which  proceed  from  the  thalamus  and  traverse  the  lenticular  nucleus.  On  the  right,  fibres  to  the 
nucleus  caudatus  and  to  the  putamen  of  the  lenticular  nucleus. 


PATHS    OF   CONDUCTION. 


137 


from  the  corpus  geniculatum  laterale,  the  chief  end-station  of  the  tractus  opticus,  and 
from  the  pulvinar  thalami,  fibres  from  the  superior  colliculus  to  the  cortex  not  being 
authenticated. 

3.  Fibres  passing  from  the  cortex  of  the  auditory  centre  to  the  inferior  colliculus 
and  to  the  corpus  geniculatum  mediale  and,  reversed,  from  the  latter  to  cortex.  As  in 
the  case  of  the  superior  colliculus,  so  also  in  that  of  the  inferior,  the  presence  of  a  quad- 
rigemino-cortical  tract  is  unproven. 

4.  Fibres  passing  from  the  cortex  (frontal  lobe,  regio  opercularis)  to  the 
nucleus   ruber. 

5.  T\^^  foryiix  passing,  as  the  equivalent  of  a  bundle  of  the  corona  radiata,  from 
the  hippocampus  to  the  diencephalon,   the  fibres  ending  within  the  corpus  mamillare. 

B.     Long   Tracts. 

The  fibres  pass  from  the  cortex  through  the  internal  capsule  to  the  crusta  or  basis 
pedunculi  cerebri,  to  end  within  the  pons,  the  medulla  oblongata  and  the  .spinal  cord. 
The  chief  tracts  are  : — 

I.  The  frontal  pontile  tract.  The  fibres  arise  within  the  cortex  of  the  fron- 
tal   lobe,    traverse    the    posterior    part    of    the    anterior    limb    of    the    internal    capsule 


Fronto-ponille  tract 


Cfrebelhtni.  vlure 
pontiii  fibres  tnd 


Fig.  130. — The  long  projection  tracts 


form   the   inner    fifth    of    the    basis    pedunculi    and    end    within    the    pons    in    the    pon- 
tile   nucleus. 

2.  The  occipito-temporal  pontile  tract.  The  fibres  arise  within  the  cortex  of  the 
occipital  and  temporal  lobes,  traverse  the  posterior  segment  of  the  internal  capsule,  form 
the  outer  fifth  of  the  basis  pedunculi  and  end  within  the  pons  in  the  pontile  nucleus. 
The  tractus  corticis  ad  pontem  further  is  joined  by  the  tractus  ponto-cercbellares ,  con- 
necting the  pons  with  the  cerebellum  (Figs.    130  and   133). 


138 


THE   FIBRE-TRACTS. 


3.  The  motor  trad.  The  fibres  arise  within  the  cortex  of  the  precentral 
convolution  and  the  paracentral  lobule,  pass  through  the  knee  and  anterior 
two-thirds  of  the  posterior  limb  of  the  internal  capsule,  form  the  middle  three- 
fifths  of  the  basis  pedunculi,  and  continue  to  the  medulla  oblongata  and  the 
spinal  cord.  The  entire  motor  tract  comprises  the  cortico-bjilbar  and  corticospinal 
tracts  (Fig.   132). 

a.  The  cortico-hdbar  tract  or  tract  of  the  motor  cerebral  nerves.  The  origin  of 
the  fibres  is  known  for  only  the  facial  and  hypoglossal  nerves,  the  fibres  of  which 
arise   within    the    cortex    of    the    lower    part  of    the    precentral   convolution.      The    tract 


Cerebellum,  ending  of 
pontile  fibres 


'dnl  decussation 


Lateral  pyrnmidiil  tract 


Spinal  cord 
Fig.  131. — Long  projection  tracts. 


passes    through    the   knee    of    the    internal    capsule    to    the    basis    pedunculi    cerebri   and 
ends    in    the    nuclei    of    the    motor    nerves    of    the    opposite   side. 

b.  The  corticospinal  tract  or  tract  of  the  motor  spinal  nerves.  The  fibres  of  this 
path,  also  known  as  the  tractus  cerebrospinalis  or  the  pyramidal  tract,  take  origin  in 
the  cortex  of  the  lobulus  paracentralis  and  of  the  upper "  and  middle  parts  of  the  motor 
region  of  the  precentral  convolution,  traverse  the  anterior  two-thirds  of  the  posterior 
limb  of  the  internal  capsule,  and  continue  through  the  basis  pedunculi  and  the  pons  to 
the  medulla  oblongata.  At  the  transition  of  the  medulla  to  the  spinal  cord,  the  fibres  of 
the  pyramidal  tract  cross  to  the  opposite  side,  forming  the  pyraitiidal  decussation.  The 
latter,  however,   is  not  complete,   since    a  small    portion    of  the  fibres  continues  uncrossed 


PATHS    OF   CONDUCTION. 


139 


in  the  anterior  column  of  the  spinal  cord  as  the  fasciculus  cerebro-spinalis  anterior  ox 
anterior  pyramidal  tract.  The  termination  of  these  fibres  is  within  the  anterior  horn  of 
the  spinal  cord  and,  moreover,  in  the  anterior  cornu  of  the  opposite  side,  the  fibres 
crossing  through  the  anterior  commissure.  The  larger  part  of  the  fibres  crosses  to  the  oppo- 
site side,  and  descends  in  the  lateral  column  of  the  spinal  cord  as  the  fasciculus  cerebro- 
spinalis  lateralis  or  lateral  pyramidal  tract,  to  end  in  the  anterior  horn  of  the  same  side. 


Curtka-hiillitir  truH 


CnrtUo-spinal  tract- 


Antfrior  p}  r„midat  tract 


Lateral  pynunidal  tract 


N.  glossppharyitgeus  and  1 
{viotor  part) 


Fig.  132. — C'ortico-bulbar  and  cortico-spinal  tracts. 


The  course  of  the  motor  tract  explains  the  fact,  that  movements  induced  by 
stimulation  of  the  motor  cortical  region  occur  chiefly  in  the  muscles  of  the  opposite 
half  of  the  body,  or  that  injury  of  the  central  neurones  of  the  motor  tract  is 
followed  by  paralysis  of  the  muscles  of  the  opposite  half  of  the  body.  Such 
paralyses  of  one  side  (hemii>legiaj  are  usually  caused  by  lesions  within  the  capsula 
interna,  less  frequently  by  lesions  within  the  cerebral  peduncle  or  the  pons.  Since 
the  speech-tract  takes  its  origin  within  the  left  hemisphere,  lesions  of  the  motor  paths 
within  the  left  hemisphere,  or  right-sided  hemiiilcgias,  are  usually  associated  with 
disturbances  of  speech. 


140 


THE    FIBRE-TRACTS. 


Tract,  cerebro-spinalis  ant. 


Fig.   133. — Motor  tract   (red)  and    the  frontal    and    occipito-temporal    pontile  tracts  (blue);    these  paths   are  continued  by 
the  ponto-cerebellar  tract  (also  blue). 


PATHS    OF   CONDUCTION. 


Tract,  certhro-spinnlis 


Medulla  oblonga^a 


Tract   crrtbrotfinalis  ant. 


Medulla  otlongala 
Nuclei  funicu/.post. 


Tract,  cfrebro-spinalis  Int. 


Medulla  spinalis 
P.C.   .34.-Mo,or  .ract   (red)  and  the  frontal   (/■)  „„d  the  occipito-tcmporal   (OT)  pontile  tract   (blue). 


142 


THE    FIBRE-TRACTS. 


In  Fio.  136,  the  course  of  tlie  motor  tract  is  schematically  represented  to  explain 
the  most  important  forms  of  paralysis.  In  total  hemiplegia,  hemiplegia  completa  (Fig. 
136,  a),  the  destruction  of  an  entire  descending  motor  tract  from  one  hemisphere  is 
concerned.  In  such  cases,  the  lesion  usually  lies  within  one  motor  tract  somewhere 
along  the  brain-stem  between  the  internal  capsule  and  the  pyramidal  decussation  in 
the  medulla  oblongata,   since  within  this  stretch   all  the  descending  motor  fibres  are  com- 


^,  Fronto-tlmlattnc  fbr 


, —  FrcKlo-jtciiiile  tract 

NV^                     J     \  Cortico-hnlhar  tract 

1    A  A ^ V"        (77/.  XIT) 

lenr.        \V 

Cortfco-sjfiniil  tract 

mus    N>'-— — -, '*>'     '---^      ^'"■'"'' 

r--  Corizco-sJ>inal  tract 
'  (leg) 

T--,  Tegtnental  trrct 
\  ise,is,^ry  tract) 

^^  OcciJ>ito-tc}j:/>t^ro 
JfcntUc  tract 


bourse  of  the  tracts  through  the  internal  capsule. 


pressed  into  a  field  of  small  area.  Most  frequently  the  lesion  is  situated  within 
the  internal  capsule  (knee  and  anterior  two-thirds  of  the  posterior  limb"),  less  fre- 
quently within  the  cerebral  peduncle  and  the  pons.  If  in  a  lesion  of  the  motor 
tract  within  the  internal  capsule  the  knee  of  the  capsule  remains  uninvolved,  the 
facial  and  hypoglossal  nerves  do  not  share  in  the  paralysis,  such  condition  con- 
stituting hemiplegia  incompleta  (^Fig.  136,  b^.  In  case  the  lesion  be  located 
within  the  region  of  the  cerebral  peduncle,  the  emerging  fibres  of  the  oculomotor 
nerve  are  often  also  implicated.  Under  such  conditions  a  homolateral  oculomotor 
paralysis    exists    in     conjunction    with     the     crossed     hemiplegia,    the    condition    being 


PATHS   OF   CONDUCTION. 


143 


designated  as  hemiplegia  alternans  oculomotoria,  or  Weber's  paralysis  (Fig.  136,  c). 
Hemiplegia  alternans  is  also  encountered  in  affections  of  the  pons  and  in  lesions 
within  the  range  of  the  medulla  oblongata.  Thus,  in  pontile  lesion,  paralysis 
of  the  extremities  on  one  side  occurs  with  paralysis  of  the  facial  nerve  on  the 
other— hemiplegia  alternans  facialis  or  Gubler's  paralysis  (Fig.  136,  d).  Further 
combinations  are :  crossed  limb-palsy  with  homolateral  paralysis  of  the  abducens, 
or  crossed  hemiplegia  with  homolateral  hypoglossal  or  lingual  paralysis. 


Hyf0gl, 


Hypogloi 


Fig.  136. — Schematic  representation  of  the  course  of  the  motor  tract,  explaining  the  most  important 
forms  of  paralysis. 


Hemiplegias  following  complete  destruction  of  the  entire  motor  cortical  region  of 
one  hemisphere  are  rare,  by  reason  of  the  large  e.xtent  of  the  motor  centre.  Cortical 
diseases  are  more  frequently  limited  to  circumscribed  areas  and  paralyses  resulting 
from  cortical  lesion  are  confined,  as  a  rule,  to  particular  portions  of  one-half  of 
the  body.  In  such  cases  one  speaks  of  monoplegia,  or,  more  definitely,  as 
monoplegia  cruralis,  monoplegia  brachialis,  or  monoplegia  facialis,  according  to  the 
involvement  of  the  motor  centre  for  the  leg,  arm,  or  face  respectively.  Such 
palsies  are  frequently  associated  with  sudden  seizures  of  convulsions  (cortical  or 
Jacksonian    epilepsy). 


144  THE    FIBRE-TRACTS. 

A  lesion  of  both  pyramidal  tracts  descending  in  the  anterior  and  lateral  columns  of 
the  spinal  cord  leads  to  paraplegia  or  paralysis  of  both  upper  or  lower  extremities  (Fig. 
136,  f,  g') — paraplegia  brachialis  or  superior  and  paraplegia  cruralis  or  inferior.  In  very 
rare  cases,  the  lesion  may  involve  the  pyramidal  decussation  in  such  manner,  that  the 
fibres  for  one  extremity  are  interrupted  above  and  those  for  the  other  below  their  place 
of  crossing.  In  such  cases  hemiplegia  cruciata  results,  that  is,  paralysis  of  the  arm  on 
one  side  and  of  the  leg  on  the  other  (Fig.    136,  e). 


RADIATIO  CORPORIS    STRIATI. 

The  corpus  striatum  is  divided  by  the  internal  capsule  into  two  parts,  the  nucleus 
caudatus  and  the  nucleus  lenticularis.  The  last-named  nucleus  is  subdivided  into  a  lateral 
portion,  the  piitameti,  and  a  medial,  the  globus  pallidiis,  the  latter,  in  turn,  exhibiting 
smaller  segments.  The  separation  of  the  lenticular  nucleus  into  the  individual  components 
is  efifected  by  white  fibre-sheets,   the  laminae  medullares. 

CONNECTIONS   OF   THE   CORPUS   STRIATUM. 

a.  Fibres  arising  within  the  cortex  pass,  as  fibres  of  the  corona  radiata,  to  ttie 
nucleus  caudatus  and  the  nucleus  lenticularis. 

b.  Fibres  from  the  nucleus  caudatus  and  the  putamen  of  the  nucleus  lenticularis 
pass  to  the  thalamus  and  the  regio  subthalamica. 

The  fibres  from  the  caudate  nucleus  traverse  the  internal  capsule  and  reach  the 
globus  pallidus,  while  those  from  the  putamen  pass  directly  to  the  globus  pallidus  and 
then  run,  together  with  those  from  the  caudate  nucleus,  to  the  thalamus — radiatio  sirio- 
thalamica. 

Fibres,  which  course  ventrally  and  are  augmented  by  those  coming  from  the  globus 
pallidus,  pass  medially  along  the  base  of  the  lenticular  nucleus  to  the  subthalamic  region 
— radiatio  strio-subthalamica.  These  fibres  form  the  a7isa  lentictilaris  and  come  into  rela- 
tion partly  with  the  ventral  portion  of  the  thalamus  and  partly  with  the  corpus  subtha- 
lamicum  or  corpus  Luysi  and  with  the  nucleus  ruber.  Some  fibres  pass  still  lower,  as 
far  as  the  mid-brain,  to  the  inferior  colliculi  of  the  corpora  quadrigemina  and  the 
substantia  nigra. 

The  ansa  lenticularis,  together  with  the  inferior  stalk  of  the  thalamus  which  conveys 
chiefly  fibres  from  the  temporal  lobe  to  the  ventral  and  medial  parts  of  the  thalamus, 
forms  the  ansa  pedujicularis  (Fig.    129). 

FIBRE-PATHS  OF  THE  RHTINENCEPHALON. 

I.    PERIPHERAL  TRACT. 

This  extends  from  the  olfactory  mucous  membrane  to  the  bulbus  olfactorlus.  The 
impulse  is  conducted  by  the  peripheral  processes  of  the  intraepithelial  bipolar  olfactory 
cells  to  the  latter,  and  thence,  by  their  central  processes,  Jila  olfactoria,  to  the  glomeruli 
olfactorii. 


PATHS    OF  THE    RHINENCEPHALON. 


145 


2.    CENTRAL   TRACT. 

A.  Connection  of  the  bulbus  olfactorius  with  the  primary  centres.  Within 
the  glomeruH,  the  impulse  is  transferred  to  the  oh'actor>-  brush  of  the  mitral  and  brush 
cells;  it  then  reaches  the  mitral  or  brush  cells  and  thence,  by  means  of  their  a.xones,  is 
conducted  centrally  to  the  primary  centres  (Fig.  137).  The  bulbus  olfactorius  is,  as  it 
were,    an    intercalated   ganglion,    being    the   end-station    of    the    peripheral    tract    and    the 


Gnnglion  dorsale  et  pro- 
fundnnt  i^gin-'itf' 


xUrp^diinciildre 


Fig.  137.— Fibr 


^-tracts  of  the  rhinencephalon.      Peripheral  tract:    olfactory  mucous  membrane  to  olfactory  bulb.     Central 
tract :  connection  of  the  olfactory  bulb  with  the  primary  centres. 


Starting  point  of  the  central  tract.  The  primary  centres  include  the  gray  substance  of 
the  tractus  olfactorius  and  of  the  trigonum  olfactorium,  the  substantia  perforata  anterior 
and  the  adjoining  part  of  the  septum  lucidum. 

B.  Connection  of  the  primary  centres  with  the  secondary  or  cortical 
centres.  The  secondary  or  cortical  centres  are  :  the  gyrus  hippocampi,  the  hippocampus 
and  the  g>Tus  dentatus.     The  connection  is  established  by  : 

a.  The  stria  olfadoria  lateralis.  The  fibres  pass  from  the  trigonum  olfactorium 
through  the  gyrus  olfactorius  lateralis  to  the  anterior  end  of  the  gyrus  hippocampi  and 
terminate  within  the  cortex  of  the  same. 

b.  The  olfactory  bundle  of  the  hippocampus  (Zuclccrkandl).  The  fibres  arise  within 
the  trigonum  olfactorium  and  the  substantia  perforata  anterior,  extend  to  the  septum 
lucidum,  are  augmented  by  fibres  from  the  septum  and  then  pass  backward  through  the 
forni.x  as  far  as  the  hippocampus. 

c.  The  stria  Lancisii.  The  fibres  pass  from  the  trigonum  olfactorium  as  the  stria 
olfactoria  medialis  towards  the  gyrus  subcallosus,  thence  over  the  corpus  callosum  and 
through  the  gyrus  dentatus  to  the  hippocampus  formation. 

According  to  Dejerine,  the  nucleics  amygdalae  is  also  a  cortical  centre.  With  this 
nucleus  a  fibre  bundle,   the    taenia    sfinicirciilaris.   stands    in    close    relation.       The    fibres 


146 


THE    FIBRE-TRACTS. 


arise  within  the  substantia  perforata  anterior  and  the  septum  lucidum,  are  augmented  by 
fibres  coming  from  the  anterior  commissure,  then  extend  convergingly  toward  the  sulcus 
i.ntermedius,  where  they  run  backward  between  the  nucleus  caudatus  and  the  thalamus 
and  end  within  the  nucleus  amygdalae.  During  the  ascending  anterior  course  of  the 
bundle,   fibres  are  given  off  at  right  angles  and  enter  the  thalamus  (Fig.    138). 

The  fornix  has  already  been  referred  to  as  the  corona  radiata  bundle  of  the 
hippocampal  formation.  The  fornix  fibres  arise  from  the  pyramidal  cells  of  the  hippo- 
campus and  the  polymorphic  cells  of  the  gyrus  dentatus.  They  extend,  first  as 
the  fimbria  and  then  as  the  posterior  limb  of  the  fornix,  toward  the  splenium  corporis 
callosi.  In  this  locality  fibres  pass  across  to  the  opposite  fornix  limb,  thus  forming 
the  fornix  transversus  or  the  conunissura  hippocampi.  During  its  course  beneath 
the    corpus    callosum,    the    fornix    receives    accessions    from    the    striae    Lancisii    in    the 


stria  Lands 


Fascicubts  olfactorbis 


TnberCHbtni  ant.  tkalam. 


Trigott 
la  olfact.   lateral. 
Siiist.  ferf.  ant. 
Nitcleiis  antygdali 

Gyms  hlppocamt>. 


Fivtbrla    Fasc.  denial. 


Fig.  138. — Fibre-tracts  of  the  rhinencephalon.     Connections  of    the    primary   centres 
or  cortical  centres. 


'ith    the    secondary 


form  of  fibres  which  pierce  the  corpus  callosum.  These  are  known  as  the  fibrae 
perforantes  and  constitute  the  fornix  longus  of  Forel.  In  addition  to  those  from 
the  striae  Lancisii,  other  fibrae  perforantes  from  the  gyrus  fornicatus  penetrate  the  cal- 
losum. The  fornix  fibres  continue  downward,  as  the  columnae  fornicis,  behind  the 
anterior  commissure.  The  majority  of  the  fornix  fibres  terminate  within  the  corpus 
mamillare — tradus  cortico-maniillaris ;  another  part  of  the  fibres,  however,  passes  to 
the  stria  meduUaris  thalami  and  with  these  to  the  ganglion  habenulae,  as  the  tradus 
cortico-habenularis . 

Some  fibres  of  the  fornix  reach  their  end-station  by  another  route.  Such  aberrant 
fibres  branch  ofl  either  above  the  foramen  Monroi,  passing  in  front  of  the  anterior 
commissure,  or  at  the  level  of  the  tuber  cinereum,  and  course  to  the  corpus  mamillare 
as  the  stria  alba  tuberis  of  Lenhossek   (page  57). 

The  paths  proceeding  from  the  corpus  mamillare,  as  well  as  those  related  to  the 
ganglion  habenulae,   may  here  be  considered. 


PATHS    OF   THE    RHINENCEPHALON. 


147 


The  corpus  mamillare  consists  of  two  nuclei  or  ganglia,  a  medial  and  a  lateral 
one.  The  medial  ganglion  forms  the  chief  portion,  while  the  lateral  ganglion  is  small 
and  arches  around  the  medial.  From  the  medial  ganglion  arises  the  fasciculus  mamillaris 
princcps,  which  extends  obliquely  upward  and  outward.  The  fibres  of  this  bundle  divide 
into  two  branches,  one  of  which  becomes  the  fasciculus  thalamo- mamillaris  or  tractus 
mamillo-ihalamicus ,  the  other  the  fasciculics  tegmento-mamillaris  or  the  tractus  mamillo- 
legmentalis  (Fig.   139). 

The  fasciculus  mamillo-thalamicus,  or  the  bundle  of  Vicq  d'Azvr,  ends  with  freely 
separated  fibres  within  the  nucleus  anterior  thalami. 

The  fasciculus  niamillo-iegmenialis,  the  tegmental  bundle  of  the  corpus  mamillare 
of  Gudden,   passes  backward   and  enters  the  tegmentum    of    the  cerebral    peduncle.      The 


Fnsc   Ugntenio-maTttillaris 
(Giiciden's  tegmental  strand) 


Fasc.  thalamo- 
{  Vtcq  d'Azyr's   bundU) 


per/orautes  (Fornix 
/aligns) 


Fornix  transversus 
Gangl.  dorsale  et  proj", 
tegm. 
Fasc,  long,  dorsal. 
(Schritz) 
Fimbria 

dentata 


Fig,   130.— Fibre-tracts  of    the 


Feduncnltis  Corp.  vtt 
Ga  tiglin  J!  in  ierp  eduncu  la  re 


Further  connections  of   the  cortical  centres.      The  tor; 
of  the  corpus  mamillare. 


major  part  of  the  fibres  ends  in  a  small  ganglion,  the  ganglion  profundum  legmenfi,  and 
in  the  neighboring  gray  substance  of  the  Sylvian  aqueduct,  some  fibres  branching  off  to 
the  posterior  longitudinal  fasciculus,  while  others  are  supposed  to  extend  as  far  as  the 
formatio  reticularis  of  the  pons. 

The  pedunculus  corporis  mamillaris  has  its  origin  within  the  lateral  ganglion  of  the 
mammillary  body.  The  bundle  courses  within  the  tegmentum  and  ends  in  the  ganglion 
dorsale  tegmetiti  and  in  the  surrounding  gray .  substance.  Fibres  are  also  described  as 
reaching  the  vicinity  of  the  medial  fillet.  The  dorsal  longitudinal  bundle  of  Schiitz 
arises  within  the  dorsal  tegmental  nucleus  and  the  central  gray  substance  (Fig.    139). 

Concerning  the  course  and  destination  of  these  bundles  which  pass  from  the  corpus 
mamillare  to  the  tegmental  region,  we  are  by  no  means  sufficiently  informed.  According 
to  other  findings,  also  ascending  bundles  run  within  the  pedunculus  corporis  mamillaris; 
these  are  said  to  arise  within  the  tegmentum  from  the  ganglion  profundum,  ;is  well  as 
from  the  fillet-layer,   and  to  end  within  the  cor[)US  mamillaie. 


148  THE    FIBRE-TRACTS. 

The  dorsal  lo7igitudinal  bundle  of  Schiitz  (Kolliker's  dorsal  gray  longitudinal  bun- 
dle, Bechterew's  dorsal  longitudinal  bundle  of  the  central  gray  substance)  is  not  to  be 
confused  with  the  strand  commonly  designated  as  the  posterior  longitudinal  bundle.  The 
longitudinal  bundle  of  Schiitz  extends  through  the  gray  substance  of  the  entire  brain- 
stem and  is  connected  with  the  nuclei  of  all  the  cerebral  nerves  and  many  other  ganglia. 
It  is  termed  the  fasciculus  loyigitudinalis  dorsalis,  while  the  ' '  posterior  longitudinal 
bundle"   is  designated  as  the  fasciculus  longitudinal  is  medialis. 

The  majority  of  the  fibres  of  the  stria  medullaris  thalami  end  within  the gangliori  habenulae. 

The  stria  medullaris  thalami  conveys  : 

a.  Fibres  coming  from  the  fornix — tractus  cortico-hahenularis. 

b.  Fibres  coming  from  the  septum  lucidum  and  from  the  area  olfactoria — tractus 
olfacto-habeniilaris. 

c.  Fibres   coming   from    the    interior    of    the    thalamus — tractus    thalanto-habenularis. 


stria  tjtalami 


Trnctns  cortico-hnbetinlaris 


Sept  lucid. 


Sitbstaittia  perf.  ant,  (Area  olfactoria-) 


Fig.  140. — Fibre-tracts  of   the  rhinencephalo 


habenulae 


c  trausversus 
GaJtglio7i  dorsale  et  prof 

teginejiti 
Fasc.  lott^.  dorsal 
—  Sckutz  — 


Fasc.   retrofle: 
—  ISIeyiteri  — 
Fasc.  haben.  Gangl.  tnterped. 
Gangl.  interped. 


Further  connections  of   the  cortical  centres, 
of  the  ganglion  habenulae. 


The  fibres  of  the  stria  thalami  which  do  not  end  within  the  ganglion  habenulae 
traverse  the  latter  and  enter  the  commissura  interhabenularis — a  bundle  of  transverse  fibres 
lying  in  front  of  the  glandula  pinealis.  Some  of  these  fibres  end  in  the  ganglion  of  the 
opposite  side,  others  pass  to  the  roof  of  the  mid-brain,  especially  to  the  superior  coUiculus, 
while   still    others,    perhaps,    come    into    relation   with    the    posterior    longitudinal    bundle. 

Within  the  ganglion  habenulae,  the  fasciculus  retroflexus  of  Meynert  takes  its 
origin.  This  bundle  ends  within  the  substantia  perforata  posterior,  in  the  region  imme- 
diately in  front  of  the  pons,  in  a  small  nucleus,  the  ganglion  iiiterpedunculare  of  Gudden. 
The  bundle  is  called,  therefore,  also  the  tractus  habcnulo-peduncularis. 

Within  the  ganglion  interpedunculare  arises  the  tegmental  tract  of  the  interpedun- 
cular ganglion.  The  fibres  pass  dorsalward  as  far  as  the  central  gray  to  end  partly  in  the 
ganglion  tegmenti  profundum  and  partly  in  the  ganglion  tegmenti  dorsale  and  the  surround- 
ing central  gray  substance.      Here  joins,  in   turn,   the  dorsal  longitudinal  bundle  of  Schiitz. 


PATHS   OF  THE    RHINENCEPHALCN. 


149 


3.  Connection  of  the  primary  centres  of  the  two  sides. — The  fibres  arise 
within  the  cortex  of  the  tractus  olfactorius  and  pass,  forming  the  pars  olfadoria  of  the 
anterior  commissure,  to  the  tractus  of  the  opposite  side.  Here  they  end,  partly  within 
the  granule-layer  and  within  the  locality  of  the  olfactory  glomeruli  of  the  bulbus. 

4.  Further  connections  of  the  primary  centres. ^Direct  fibres  pass  to  the 
tuber  cinereum,  to  the  corpus  mamillare,  to  the  lower  lying  brain-segments  and  to  the 
spinal  cord.  They  form  the  olfactory  radiation  to  the  diencephalon  and  to  the  mid- 
brain— tractus  olfacto-incsenccphalicus,   the  basal  olfactory  bundle  of  Wallenberg. 

The  tract  of  fibres  passing  to  the  corpus  mamillare  is  further  joined  by  the  fibre- 
system  of  the  mammillary  body,  whereby  further  relations  with  the  thalamus  and  the 
mid-brain  are  established.  A  similar  connection  of  the  primary  centres  is  effected  through 
the  fibre-system   of  the  ganglion  habenulae. 


Fasc.  tegmento-\ 
(Gitdden's  tegmental  strand) 


Fasc.  thnlamo-. 
{  Vicq  d'Azyr's  bundle) 


Peiiunculus  corpor.  mnmillaris 
Ca  tigli'on  iuterpediinculare 


-Fibre-tracts  of  the 


rhinencephalon. 
Wallenberg 


Further   connections  of  the  primary  centres, 
nd  the  system  of  the  corpus  mamillare. 


Basal  olfactory  bundle  of 


Ascending  fibres  from  the  lower  brain-segments,  as  strands  from  the  vicinity  of  the  end- 
nucleus  of  the  trigeminus,  are  also  credited  with  terminating  within  the  primary  olfactory 
centres.  Since  terminal  arborizations  of  the  trigeminus  are  found  within  the  regio  olfactoria 
of  the  nasal  mucous  membrane  and  since  this  nerve,  perhaps,  also  shares  in  the  conduction 
of  olfactory  stimuli,  it  is  not  impossible  that  impulses  may  be  carried  from  the  olfactory 
region   tfi  the   cortical  olfactory  centre  by  means  of  the  ascending  central  trigeminal  tract. 

5.  Connection  of  the  cortical  centres  of  the  two  sides. — This  is  accom- 
plished by  the  fibres  of  the  forni.x  transversus,  and,  perhaps,  by  the  pars  interhemi- 
sphacrica  of  the  anterior  commissure. 

6.  Further  connections  of  the  cortical  centres. — The  fornix  perip/iericus  of 
Arnold,  or  the  cingidutn,  is  to  be  regarded  as  an  association  bundle  of  the  rhinencephalon. 
It  appears  as  an  arcuate  bundle,  which  surrounds  the  rostrum,  knee,  body  and  splenium 
of  the  corpus  callosum  ;  at  the  isthmus  it  becomes  narrow  and  expands  toward  the  front 
end  of  the  uncus.  It  consists  of  fibres  which  do  not  extend  the  entire  length  of  the 
tract,    but  form   larger  or   shorter  strands,    whose   crooked  ends   radiate   within   the  white 


I50  THE    FIBRE-TRACTS. 

substance  of  the  neighboring  convolutions.  The  cingulum  appears  to  be,  therefore,  not 
properly  an  association  bundle  of  the  rhinencephalon,  but  an  association  strand  of  the 
different  convolutions  of  the  medial  surface  of  the  hemisphere  (Fig.  126). 

Reviewing  the  entire  fibre-tracts  of  the  rhinencephalon,  we  recognize,  in  the  first 
place,  that  a  centripetal  projection  path  conducts  the  impulse  from  the  regio  olfactoria  to 
the  primary  centres  and  thence  to  the  cortical  centre  proper  ;  secondly,  that  a  centrifugal 
projection  path  transfers  impulses  from  the  cortical  olfactory  centre  to  subcortical  centres 
(corpus  mamillare,  ganglion  habenulae),  from  which  latter  then,  by  means  of  further 
paths,  still  other  nuclei  may  be  influenced.  Thirdly,  the  tracts  that  arise  within  the 
primary  centres  and  pass  directly  to  the  subcortical  ganglia,  constitute  special  reflex  paths, 
and  by  means  of  these,  in  consequence  of  the  transference  of  the  impulse  to  the  most 
diverse  nuclei  of  the  brain-stem,  as  the  nuclei  of  the  motor  nerves,  the  most  varied 
reflex  movements  may  be  induced.  Finally,  the  peripheral  and  central  districts  of  the 
rhinencephalon  of  both  hemispheres  are  brought  into  relation  with  each  other  by  means 
of  certain  systems  of  commissural  fibres  ;  through  the  fornix  periphericus,  the  central 
district  is  also  connected  with  the  adjoining  regions  of  the  pallium. 

CONDUCTION   PATHS  OF  THE  DIENCEPHALON. 

The  connections  which  unite  the  diencephalon  with  other  parts  of  the  brain  have, 
in  large  part,  been  presented  in  the  preceding  section.  To  these  belong,  in  the  first 
place,  the  tradus  co7'tico-thalaniici  and  thalamo-corticales — the  thalamic  peduncles — of  which 
the  tegmental  tract  and  the  optic  radiation  may  be  again  mentioned  as  of  especial 
importance.  Others  to  be  recalled  are  those  fibre-tracts  which  unite  certain  parts  of  the 
olfactory  brain  with  the  thalamencephalon  and  the  hypothalamus — fornix,  stria  medullaris, 
basal  olfactory  bundle,  which  tracts  are  joined,  moreover,  by  those  passing  from  the 
diencephalon  to  the  mid-brain — fasciculus  mamillo-tegmentalis,  pedunculus  corporis  mamil- 
laris,  tractus  habenulo-peduncularis.  Further,  the  connections  which  join  the  corpus 
striatum  with  the  thalamus  and  with  the  subthalamic  region — the  radiatio  strio-thalamica 
and  strio-subthal arnica. 

Within  the  pulvinar  thalami  and  the  corpus  geniculatum  laterale,  which  parts, 
together  with  the  superior  colliculus,  constitute  the  primary  visual  centre  (page  172),  the 
fibres  of  the  tractus  opticus  end.  The  corpus  geniculatum  mediale,  with  the  inferior 
colliculus,  constitutes  the  primary  auditory  centre,  since  within  these  parts,  particularly 
within  the  medial  geniculate  body,  the  fibres  of  the  lateral  fillet  end  ;  the  latter,  as  later 
to  be  described  (page  179),  serves  to  conduct  the  impulses  from  the  end-nuclei  of  the 
acoustic  nerve  farther  centrally  and,  hence,  represents  the  primary  auditory  tract.  From 
the  corpus  geniculatum  laterale  and  the  pulvinar  thalami,  the  optic  radiation  passes  to 
the  cortex  of  the  visual  centre  in  the  occipital  lobe  ;  from  the  corpus  geniculatum  mediale, 
the  secondary  auditory  tract  passes  to  the  cortex  of  the  auditory  centre  in  the  temporal  lobe. 

Within  the  thalamus,  moreover,  end  certain  fibre-strands  which  come  from  the 
cerebellum,  the  medulla  oblongata  and  the  spinal  cord.  Bundles  of  fibres,  from  the 
nucleus  dentatus  and  in  small  part  also  from  the  nucleus  tecti,  pass  forward  from  the 
cerebellum,  constituting  collectively  the  superior  cerebellar  pedu'}wle.  The  larger  part  of 
these  fibres,  after  decussation,  reaches  the  nucleus  ruber  in  the  tegmentum  of  the  mid- 
brain and  there  ends — tractus  cerebello-tegmentalis ;  the    smaller  part    of  the  fibres  passes 


PATHS    OF  THE    MESENCEPHALON.  151 

directly  to  the  thalamus,  joining  such  as  come  from  the  red  nucleus — tradus  rubro- 
thalamims.  The  fibres  proceeding  from  the  medulla  oblongata  and  from  the  spinal  cord 
form  the  large  ascending  sensory  path,  tractus  spina-  et  bulbo-thalamicus ,  the  detailed 
origin  and  course  of  which  will  be  later  considered.  For  the  present  suffice  it  to  note, 
that  this  tract,  known  as  the  ^nedial  fillet  or  lemniscus  medialis,  carries  fibres  from  the 
spinal  cord,  the  nuclei  of  the  posterior  column  and  the  end-nuclei  of  the  sensory 
cerebral  nerves.  Its  termination  is  principally  within  the  lateral  nucleus  and  the  centrum 
medianum  of  the  thalamus.  Impulses  from  the  spinal  cord,  the  nuclei  of  the  posterior 
column  and  the  olivary  nucleus  of  the  medulla  may  reach  the  thalamus  also  by  way  of 
the  cerebellum  and  the  superior  cerebellar  peduncle.  These  paths  are  shown  in  Figs. 
142  and  147.  The  tractus  thalamo-olivaris  is  a  spinalward  coursing  path,  that  connects 
the  thalamus  with  the  olive  of  the  medulla  (Fig.  147);  it  is  also  termed  the  central 
tegmental  tract.  Since  the  olive  sends  fibres  to  the  cerebellum,  impulses  from  the 
thalamus  may  be  conveyed  to  the  cerebellum  by  this  tract. 

Probably  still  other  paths  proceed  from  the  thalamus  downward,  to  end  within  the  mid- 
brain, the  pons,  the  medulla  and  the  spinal  cord.  Such  connections,  however,  are  not  accu- 
rately determined.  The  descending  tractiis  thalamo-spinalis  accompanies  the  tractus  rubro- 
spinalis  to  the  spinal  cord,  within  which  it  courses  in  the  dorsal  part  of  the  lateral  column. 

Finally,  mention  must  be  made  of  the  system  of  the  ventricular  gray,  which  gray 
substance  covers  the  medial  surface  of  the  thalamus  and  hypothalamus  and  the  floor  of 
the  third  ventricle  and  is  continuous  with  the  gray  substance  surrounding  the  aquaeductus 
Sylvii  and  investing  the  floor  of  the  fourth  ventricle.  The  fibres  from  the  cells  situated 
within  this  gray  substance  pass  to  all  the  thalamic  nuclei,  while  delicate  longitudinal 
strands  proceed  caudalward  through  the  gray  in  the  medulla  oblongata  and  into  the 
spinal  cord.  This  system  of  longitudinal  fibres,  which  has  been  already  noticed  in 
connection  with  the  fibre-tracts  of  the  rhinencephalon,  is  the  fasciculus  longitudinalis 
dorsaliSy  or  dorsal  longitudinal  bundle  of  Schutz,  and  is  closely  connected  with  the 
nuclei  of  the  cerebral  nerves  and  other  ganglia.  Concerning  the  significance  of  the 
entire  system,  we  are,  at  present,  insufficiently  informed.  According  to  Edinger,  it  is 
not  unlikely,  that  all  these  nuclei  and  fibres  constitute  a  central  apparatus  of  the  sympathetic. 

CONDUCTION    PATHS  OF  THE  MESENCEPHALON. 

The  mesencephalon,  which,  as  the  smallest  of  the  brain  segments,  includes  the 
quadrigeminal  region  and  the  cerebral  peduncles,  is  traversed  by  several  main  tracts,  on 
the  one  hand,   and  is  the  termination   or  the   origin  of   many  fibre-strands,   on  the  other. 

I.  The  chief  tracts  traversing  the  mid-brain  are  those  which  descend  from 
the  cortex  of  the  cerebral  hemispheres,  already  described  in  connection  with  the  conduc- 
tion paths  of  the  telencephalon,  namely :  the  fro7ital  pontile  tract,  the  occipito-temporal 
pontile  tract  and  the  motor  tract.  These  three  chief  paths  pass  through  the  basis  pedun- 
culi  or  crusta,  the  frontal  fibres  occupying  the  medial  and  the  occipito-temporal  the 
lateral  part,  while  the  motor  tract  appropriates  the  middle  portion  of  the  crusta  between  the 
pontile  tracts.  An  additional  traversing  path  is  the  sensory  tract  or  medial  fillet,  which 
ascends  from  the  spinal  cord,  the  nuclei  of  the  posterior  columns  and  the  end-nuclei  of  the 
sensory  cerebral  nerves  and  continues  to  the  thalamus,  joined  by  the  tegmental  tract  that 
unites    the    thalamus   with    the    sensory    region  in  the    cortex  of    the   parietal  lobe.     This 


152 


THE    FIBRE-TRACTS. 


ascending  sensory  tract,  however,  does  not  pass  through  the  crusta  of  the  cerebral  pe- 
duncle, but  through  the  tegmental  area.  Of  the  additional  traversing  paths,  the  tractus 
thalamo-olivaris  or  the  central  tegmental  tract  deserves  special  mention. 


Tractus  corticn-pontl. 
Tract.  tecto-Jionti 

Tract,  cerebro-spinalis 
Tractus  tecto-splnalis  and  spltw-tectalls 


ytl_^J. I Tractus  cerebello 

,^^_y    ^y^l        J  tegTttentalis 

denfaf.cerebelli, 


-    Tractus  rubro-spinalis  (Monakowi 


Nuclei  fume.  post. 


Fig    142. — Schematic  representation  of  the  chief  connections  of  the  mid-brain  and  of  the  tracts  passing 
through  the  mid-brain. 


II.     Tracts  ending  within  the  mid-brain: 

a.  Within  the  regioti  of  the  superior  colliculus  end  some  fibres  of  the  optic  tract ; 
within  the  inferior  colliculus,  the  fibres  or  collaterals  of  the  lateral  fillet,  which  latter 
represents  the  primary  auditory  path. 


PATHS    OF   THE    MESENCEPHALON.  153 

b.  Within  the  quadrigeminal  region  end  additional  fibres  from  the  cortex,  tradus 
cortico-tcdalcs — in  the  superior  colHculus  principally  fibres  from  the  occipital  lobe  and  in 
the  inferior  colliculus  those  from  the  temporal  lobe  ;  further  fibres  are  those  of  the  tradus 
spino-tedalcs,  which  ascend  from  the  lateral  column  of  the  spinal  cord. 

c.  Within  the  nudeus  ruder  end,  first,  fibres  from  the  cortex  (frontal  lobe,  regio  opercu- 
iaris)  and  from,  the  corpus  striatum;  second  and  most  important,  fibres  from  the  cerebellum., 
The  last  take  their  origin  in  the  nucleus  dentatus,  in  small  part  also  in  the  nucleus  tecti,  and, 
perhaps,  also  in  the  cortex  of  the  cerebellum,  and  form  the  brachia  conjunctiva  or  superior 
cerebellar  peduncles.  After  decussation  within  the  tegmentum  of  the  mid-brain,  the  fibres 
end  in  the   nucleus  ruber  and,  in  part,  also  in  the  thalamus — tradus  cerebello-tegmentalis. 

d.  Small  individual  fibre-bundles,  which  in  part  end  in  the  mid-brain  and  in  part 
run  still  farther  caudally — the  tegmental  bundle  of  the  ganglion  interpedunculare,  fibre- 
strands  from  the  corpus  mamillare  and  from  the  posterior  longitudinal  bundle. 

III.  Tracts  arising  within  the  mid-brain; 

a.  Tradus  tedo-bulbaris  et  tedo-spinalis,  fibre-strands  which  arise  from  the  deep 
medullary  substance  of  the  corpora  quadrigemina,  cross  (Meynert's  tegmental  decussation) 
and  terminate  within  the  nuclei  of  the  medulla  oblongata  and  within  the  anterior  and 
lateral  columns  of  the  spinal  cord.  Since  fibres  of  the  visual  tract  end  within  the 
superior  colliculus  and  those  of  the  auditory  tract  within  the  inferior  colliculus,  the 
impulses  brought  to  the  mid-brain  by  these  paths  may  be  conveyed  to  the  medulla  and 
the  cord  by  the  tecto-bulbar  and  the  tecto-spinal  tract  respectively.  These  paths,  there- 
fore, are  also  called  the  visuo-acoustic  reflex  trad.  The  tract  leading  to  the  anterior 
column  is  known  also  as  the  fasciculus  longitudinalis  praedorsalis,  since  the  bundle  lies 
ventral  to  the  posterior  longitudinal  bundle  in  its  course  through  the  brain-stem. 

b.  Tradus  tedo-cerebcllares,   from  the   quadrigeminal  plate  to  the  cerebellum. 

c.  Tradus  tedo-pontinus  {Mu?tzer),  a  small  fibre-strand  that  arises  within  the 
quadrigeminal  region,  more  especially  within  the  inferior  colliculus,  and  ends  in  the 
pontile  nuclei  in  the  vicinity  of  the  pyramidal  tract. 

A  small  bundle,  the  tradus  tedo-reticularis  of  Pavlow,  extends  from  the  quadrigem- 
inal region  to  the  tegmentum  of  the  pons  and  ends  within  the  nucleus  reticularis  tegmenti. 

d.  Tradus  rubro-spinalis,  also  known  as  Monakow  s  bundle,  arises  in  the  red 
nucleus  of  the  tegmentum.  The  fibres  emerging  from  the  nucleus  cross  and  descend 
through  the  pontile  tegmentum  and  the  medulla  oblongata  to  the  lateral  column  of  the 
spinal  cord,   to  end  within  the  anterior  horn. 

Moreover,  the  tradus  rubro-reticidaris  includes  fibres  which  pass,  crossed  and  un- 
crossed, from  the  red  nucleus  to  the  formatio  reticularis  of  the  pons  and  of  the  medulla 
oblongata  ;  a  further  bundle,  the  tradus  ruhro-laqiiearis,  passes  from  the  red  nucleus  to 
the  nucleus  of  the  lateral  fillet. 

i\  Fasciculus  longitudinalis  medialis,  commonly  called  the  posterior  longitudinal 
bundle,  is  composed  of  fibres  taking  their  origin  in  different  places.  The  principal  fibre- 
strands  arise  from  Deiters'  nucleus  and  from  the  nucleus  of  the  pnstcrior  commissure  and 
of  the  posterior  longitudinal  bundle,  situated  in  front  of  the  oculomotor  nucleus  (p.  182). 
/.  Finally  it  must  be  noted,  that  the  oculomotor  and  the  trochlear  nerves,  as  well 
as  a  small  motor  root  of  the  trigeminus,   have  their  origin  within  the  mid-brain. 


154 


THE    FIBRE-TRACTS. 


CONDUCTION  PATHS  OF  THE  METENCEPHALON. 

Before  considering  the  individual  fibre-tracts  connecting  the  cerebellum  and  the  pons 
with  other  parts  of  the  brain  and  the  spinal  cord,  the  structure  of  the  cerebellar  cortex 
must  be  more  closely  examined. 

HISTOLOGY    OF   THE   CEREBELLAR   CORTEX. 

The  cerebellar  cortex  presents  the  following  layers  : 

1.  The  molecular  layer — the  outermost  stratum  ; 

2.  The  layer  of  Pttrkinje  cells — the  middle  stratum  ; 

3.  The  granule  layer — the  innermost  stratum. 


Furkmje  cells 


Basket  cells' '  ~ 


Mess  fib: 


Sagittal  section 
Fig.  143. — Schematic  representation  of  the  cerebellar  cortex. 

The  Purkinje  cells  send  their  richly  branched  protoplasmic  processes  or  dendrites 
into  the  molecular  layer,  while  the  axones  of  the  cells  pass  through  the  granule  layer  to 
the  white  substance  of  the  cerebellum. 

Within  the  molecular  layer,  in  addition  to  small  cortical  cells  with  short 
axones,  are  found  the  basket-cells.  The  latter  are  distinguished  by  their  axones, 
which  run  sagittally  and  parallel  to  the  surface  and  give  off  numerous  collaterals 
that  pass  inward  and  surround  the  cell-bodies  of  the  Purkinje  cells  with  basket-like 
ramifications  (Fig.    143). 

Within  the  granule  layer,  the  small  granule-cells  are  the  chief  elements.  They  are 
small  spherical  cells  with  from  three  to  five  short  dendrites.     Their  axones  pass  into  the  molec- 


PATHS    OF  THE   CEREBELLUM. 


155 


ular  layer,  «here  they  divide  into  two  branches,  that  run  parallel  to  the  surface  and  in  corre- 
spondence with  the  direction  of  the  cerebellar  convolutions  or  folia.  These  axones 
extend,  therefore,  in  the  frontal  plane  and  not,  as  do  those  of  the  basket-cells,  in  the 
sao^ittal  plane.  During  their  course,  the  branches  give  off  collaterals  which  pass  to  the 
Purkinje  cells.  In  addition  to  the  granule-cells,  Golgi  11  type  cells  occur,  whose 
dendrites  often  extend  far  into  the  molecular  layer  and  whose  axones  resolve  into 
branchings    of    unusual    richness. 

Nerve-fibres  enter  the  cortex  from  the  subjacent  white  substance.  Of  these,  the 
"  climbing  fibres'"  pass  to  the  molecular  layer  and  there  end  among  the  dendrites  of  the 
Purkinje-cells,  while  the  ''moss  fibres''  terminate  chiefly  within  the  granule  layer.  Im- 
pulses, conveyed  by  these  fibres  which  enter  the  cerebellum,  are  transferred  to  the 
different  varieties  of  cortical  cells.  In  this  connection,  it  is  worthy  of  special  note,  that 
bv  means  of  the  basket-cells  impulses  are  conveyed  in  the  sagittal  direction  and  by  means 
of   the  granule-cells   in   the  frontal   direction  and   transferred   to   numerous   Purkinje  cells. 

FIBRE-TRACTS    OF    THE   CEREBELLUM. 

All  cortical  regions  of  the  cerebellum  are  linked  together  by  means  of  arched 
fibres,  the  fibrae  arci formes.  Such  association  systems  unite  neighboring  folia  or  lobules 
of  the  cerebellum.  The  cortex,  moreover,  sends  centrifugal  fibres  to  the  nuclei — to  the 
nucleus  dentatus  and  the  nucleus  fastigii,   as  well  as  to  Deiters'    nucleus. 


Tractits  cerebello-iegiiteniales 
i  Superior  pedtmcte) 


The    chief   connections  of  the  cerebellum  are: 

1.  Tractiis  ponto-cerebellares,    composed    of    fibres    which  arise    in  the  pontile   nuclei 
and  proceed    to    the    cerebellar   hemisphere  of  the   opposite  side.     These  tracts  form  the 
middle  cerebellar  peduncle.     Since  the  ponto-cerebellar  tract  continues  the  tractus  corticis 
ad  pontem,   connecting  the  cere- 
bral    cortex     with     the     pontile 
nucleus,      impulses     are     carried 
from  the  cerebrum    to    the   cere- 
bellum.     Relations    between    the 
cerebral    cortex    and    the     cere- 
bellum may  be  further  established 
by    way    of     the    thalamus    and 
the    inferior  olive. 

Some  fibres  pass  in  the 
opposite  direction,  from  the  cere- 
bellum through  the  middle  cere- 
bellar peduncle  to  the  pons  and 
thence,  as  the  fibrae  reclae  pontis., 
dorsally  within  the  raphe  of  the 
pons  to  the  centro-lateral  micleiis 
reclicularis    iegmenli   ponlis,    thus    constituting    the    tractus    cerebello-tegmentalis    pontis. 

2.  Tractus   cerebello-legmentales,     composed    of    fibres    which  arise    in    the    nucleus 
dentatus  and  partly  in  the  nucleus  fastigii    or    roof-nucleus    of   the    cerebellum,   pass    for- 


which  pass  the  pouto-cerfhrllnr  tracts 
Fig.  144. — Fibre-tracts  of  the  cei 


156 


THE    FIBRE-TRACTS. 


ward,  decussate  in  the  quadrigeminal  region  and  end  within  the  nucleus  ruber  or  the 
thalamus.  They  constitute  the  superior  cerebellar,  peduncle  or  brachium  conjunctiva, 
the  crossing  being  known  as  the  decussation  of  the  superior  pedimcle.  These  fibre- 
bundles,  chiefly  from  the  nucleus  dentatus  cerebelli,  give  off  descending  collateral 
branches,  which  may  be  followed  as  a  special  bundle  as  far  as  the  pons  and  the 
medulla    oblongata,    where    they    probably   end    in    motor    nuclei.       In    addition    to    this 


7raciics  coTticis 
ad  pontem 


145. — Connections  of  the  cerebral  cortex  with  the  cerebellun 


nth  the  cerebral  cortex. 


robust  cerebellofugal  tract,  other  efferent  bundles  pass  caudalward  from  the  roof- 
nucleus,  of  the  same  and  the  opposite  side^  into  the  tegmental  area  of  the  medulla 
oblongata,  where  they  end  around  the  cells  of  the  substantia  reticularis.  These  fibres, 
however,  emerge  from  the  cerebellum  by  way  of  the  inferior  cerebellar  peduncle  or 
restiform  body  and  are  specially  designated  as  the  tractus  ce7-ebello-tegmentalis  bulbi, 
while  those  in  the  superior  peduncle  are  called  the  tractus  cerebello-tegnientalis 
mesencephali. 


PATHS   OF  THE   CEREBELLUM. 


157 


By  means  of  the  middle  cerebellar  peduncles,  therefore,  especially  impulses  from 
the  cerebrum  are  conveyed  to  the  cerebellum.  The  superior  cerebellar  peduncle,  on 
the  contrary,  carries  impulses  by  way  of  the  red  nucleus  and  the  thalamus  from  the 
cerebellum  to  the  cerebrum.  In  addition,  however,  by  way  of  the  tractus  cerebello- 
tegmentalis  mesencephali  (cerebellum  to  red  nucleus),  as  well  as  by  the  tractus  cerebello- 
tegmentalis    pontis    et    bulbi,    the    possibility    exists,    that    impulses    from    the    cerebellum 


Tract,  rubro-spinalis 


Fig.  146. — Tractus  cerebello-tegmentalis  mesencephali — nucleus  dentatus  cerebelli — nucleus  ruber.  Tractus  cerebello- 
tegmentalis  pontis  et  bulbi.  Tractus  rubro-reticularis  and  tractus  rubro-spinalis;  also  the  tracts  coursing  within  the 
formatio  reticularis. 

may  be  finally  transferred  to  the  motor  nuclei  of  the  cerebral  nerves  and  to  the 
gray  substance  of  the  spinal  cord.  Since  the  tractus  rubro-reticularis  passes  from 
the  red  nucleus  to  the  cells  of  the  formatio  reticularis  of  the  pons  and  of  the  medulla 
oblongata  and  the  tractus  rubro-spinalis  passes  to  the  spinal  cord,  while  other  fibres 
spring  from  the  cells  of  the  formatio  reticularis,  around  which  also  the  tractus  cere- 
bello-tegmentalis pontis  et  bulbi  end,  certain  fibre-strands  reach  far  down  into  the 
medulla  and  the  spinal  cord. 


158 


THE    FIBRE-TRACTS. 


3.  Constituents  of  the  inferior  cerebellar  peduncle,  fibres  which  come  from 
the  spinal  cord  and  the  medulla  oblongata  and  pass  to  the  cerebellum  by  way  of 
the     peduncle     or     restiform     body.       The    constitution    and    destination    of    the    latter 


Olfva 

Tractns  sptno-oUvnrls  (Hekueg)   \-A 

Tract.  spinO'Cerebellaris  ventrttlis  (Gowers)    


Tract,  cerel'ello- 
tegmentatis 


Tractns  ritbro-spinalis  [MonaknV\ 
Nuclei  /laiic.  post. 
Tract,  funic  post 


Tract,  splno  cerebellar  Is 
( Flechslg) 


alls 


Pig.   147 — Schematic  representation  of  the  chief  connections  of  the  cerebellu 


will     be     further     considered     in     connection      with      the      fibre-tracts     of     the     medulla 
oblongata    (page  170). 

The  chief  connections  of  the  pons  and  of  the  cerebellum  are  represented  in  Figs. 
144,  145  and  147.  It  is  to  be  noted,  further,  that  numerous  tracts,  descending  as  well 
as  ascending,   traverse  the  pons   (Figs.    142  and   147). 


CELL-GROUPS    OF   SPINAL   CORD. 


159 


THE  SPINAL  CORD. 

THE    GRAY    SUBSTANCE. 

E.xclusive  of  the  supporting  tissue,  the  gray  substance  consists  principally  of  nerve- 
cells  with  their  protoplasmic  and  nerve-processes  and  nerve-fibres  ending  around  the 
nerve-cells.  Topographically  regarded,  four  different  cell-groups  may  be  distinguished. 
Thus,  in  the  anterior  horn  in  the  cervical  and  lumbar  enlargements,  a  vcntro-mcdial 
and  a  ventro-lateral  and  a  dorso-mcdial  and  a  dorso-lateral  group  are  clearly  recognized  ; 
between  these  groups  lies  the  intermediate  zo7ie  or  central  field  that  borders  the 
posterior  horn. 

N^rve-processes  from  tract-cells 


Pig.  148. — Schematic  representation  of  the  different  cla 


of  cells  of  the  spinal 


Dorsal  to  the  dorso-lateral  cells,  is  situated  the  cell-group  of  the  lateral  horn, 
while  Clarke' s  coluinn  lies  somewhat  medial  to  the  transition  of  the  intermediate  zone 
into  the  posterior  horn. 

Everywhere  within  the  posterior  horn,  mostly  small  cells  are  scattered  without 
the  definite  disposition  of  the  anterior  cornu ;  nevertheless,  also  here  different  groups 
are  defined,  as  the  basal,  the  central  and  the  marginal  cells  and  those  of  the 
substantia  Rolandi. 

In  contrast  to  this  subdivision  of  the  cord-cells  according  to  position  and  arrange- 
ment within  the  gray  suf>stance,  a  classification   according  to  the  behavior  of  their  nerve- 


i6o  THE    FIBRE-TRACTS. 

processes  is  more  appropriate  for  a  presentation  of  the  fibre-tracts.      Tfierefore,  we  divide 
the  cells  of  the  spinal  cord  into  : 

1.  Cells,  whose  axones  pass  from  the  spinal  cord.  They  lie  within  the  anterior 
horn  and  are  called  the  jnotor  anterior  horn-cells.  Their  nerve-processes  form  the 
anterior  roots  emerging  from  .the  spinal  cord. 

2.  Cells,  whose  axones  pass  into  the  'white  substance.  Within  the  latter,  the 
axone  divides  into  an  ascending  and  a  descending  branch.  The  descending  branch, 
after  a  short  course,  again  enters  the  gray  substance,  where  it  ends;  the  ascending 
branch  courses  upward  within  the  white  substance.  These  cells  are  termed  column-cells, 
of  which  two  varieties  are  distinguished  : 

a.  Cells,  whose  axones,  that  is,  ascending  branches,  pass  upward  and  as  special 
paths  connect  the  spinal  cord  with  the  brain;  such  are  ti-aci-cells. 

b.  Cells,  whose  ascending  branches  or  axones  after  a  longer  or  shorter  course 
again  enter  the  gray  substance  of  the  cord  and  serve  to  unite  different  cord-segments; 
such  are  association-cells. 

The  column-cells  may  be  further  distinguished  as  homolateral  and  contralateral. 
The  axones  of  the  former  pass  into  the  white  substance  of  the  same  side,  those  of  the 
latter  to  the  white  substance  of  the  opposite  side  by  way  of  the  anterior  commissure — 
commissure-cells.  The  column-cells  are  designated  respectively  as  anterior,  lateral  or 
posterior  column-cells  according  to  the  column  in  which  they  course.  While  the  column- 
cells  are  found  in  all  parts  of  the  gray  substance,  the  contralateral  column-cells  occur 
chiefly  within  the  base  of  the  posterior  horn  and  the  intermediate  zone.  (Commissure- 
cells  are  shown  in  the  first  and  second  cross-sections  in  Fig.    148.) 

3.  Cells  of  Golgi  II  type.  These  are  found  predominatingly  within  the  posterior 
horns  and  the  substantia  gelatinosa  Rolandi. 

The  motor  anterior  horn-cells,  whose  axones  form  the  motor  anterior  roots,  occupy 
a  special  position,  since  they  are  the  only  elements  that  send  their  axones  from  the  cen- 
tral organ  to  the  periphery.  The  column-cells  and  the  Golgi  cells,  with  their  entire 
expansions,  belong  to  the  central  nervous  system.  The  tract-cells  estabHsh  relations  between 
the  spinal  cord  and  the  higher  lying  centres  ;  the  association-cells  serve  to  transfer  an 
impulse  received  within  the  cord  to  higher  and  lower  lying  cell-complexes  ;  while  the  field 
of  activity  of  the  cells  of  Golgi's  II  type  is  limited  to  the  immediate  vicinity.  The  nerve- 
processes  of  the  association-cells  are  also  spoken  of  as  endogetious  fibres. 

THE  WHITE  SUBSTANCE. 

The  white  substance  consists  essentially  of  the  longitudinally  coursing  nerve-fibres.. 
The  following  chief  systems  of  fibres  are  distinguished  : 

a.  Fibres,  which  arise  within  the  cerebral  cortex  and  within  certain  parts  of  the 
brain,   descend  within  the  spinal  cord  and  there  end. 

b.  Fibres,  which  arise  within  the  gray  substance  of  the  spinal  cord  and  end  in 
higher  lying  parts — axones  of  the  tract-cells. 

c.  Fibres,  which  unite  particular  levels  of  the  spinal  cord — axones  of  the  association-cells. 

d.  Fibres,  which  arise  from  the  spinal  ganglia  as  continuations  of  the  posterior 
roots,   enter  the  spinal  cord  and  course  within  the  posterior  columns. 


PATHS    OF  THE   SPINAL    CORD. 


i6i 


I.  TRACTS  OF  THE  ANTERIOR  COLUMN. 

The  hactus  cerebro-spinalis  anterior  or  the  anterior  pyramidal  tract  passes  medially, 
along  the  anterior  median  fissure.  The  fibres  end,  after  crossing  in  the  anterior  commis- 
sure,  within  the  anterior  horn  of  the  opposite  side. 

The  field  of  the  anterior  pyramidal  tract  is  shared  by  fibres  that  descend  from  the 
mid-brain.  They  constitute  the  tradiis  tecto-spinalis,  ox  fasciculus  sulco-tnarginalis.  The 
fibres,  in  part,  cross  after  their  origin  in  the  corpora  quadrigemina.  A  portion  of  the 
fibres  pass  also  to  the  lateral  column  of   the  cord — traclus  tecto-spinalis  lateralis. 

BurdnchS       Coil's  Oval 

Root-zone       strand         strand     dittidle     Ventral  field 

/ 


Us 


\rea  oj  tr.  rubro-sfiinalis  - ..  _ 
Lateral  boundary  layer  — 
Tract,  sptno-thalamic 


il.udU 
.Lateral  pyravirdal  tract 


Tractus  sptno-cerebellarU  dor- 
talis  (Flecfisig) 


Tractus  spino-cerebellarts  ; 
trails  {Cowers) 


Tractus  spino-oUvaris  {Helweg) 


Anterior  root 

Anterior  ground  bundle 

Fasciculus  Tract,  vestibulo-spinalis 

sulco-marginalis 
Anterior  pyramidal  tract    s.  Tract,  tecto-spinalis 

Fig.  149- — Fibre-systems  of  the  white  substance  of  the  spinal  cord. 


At  the  \entral  border  of  the  anterior  column,  fibres  are  found  which  come  from 
Deiters'  nucleus  and  constitute  the  tractus  vestibulo-spinalis  anterior  or  the  anterior  nia?-- 
ginal  bundle. 

Lasdy,  as  an  additional  descending  path  within  the  anterior  column,  the  posterior 
longitudinal  bundle,   or  the  fasciculus  longitudinalis  tnedialis,   must  be  noted. 

The  remaining  part  of  the  anterior  column  constitutes  the  anterior  ground  bundle 
or  fasciculus  anterior  proprius.  Within  this  field  longitudinally  course  the  endogenous 
fibres,   which  serve  to  unite  different  segments  of  the  spinal  cord. 


2.  TRACT.S  OK  THE  LATERAL  COLUMN. 

The  tractus  cerebro-spinalis  lateralis  or  the  lateral  pyramidal  tract  extends  as  a 
robust  bundle  in  the  dorsal  part  of  the  lateral  column.  The  termination  of  the  fibres  is 
in  the  anterior  horn  of  the  same  side  of  the  cord. 

The  tractus  spino-cerebellaris  dorsalis  or  direct  cerebellar  trad  lies  at  the  periphery, 
lateral  to  the  pyramidal  tract.  The  fibres  arise  from  the  cells  of  Clarke's  column,  extend 
upward  within  the  lateral  column  and  pass,  as  a  constituent  of  the  restiform  body,  to  the 
cerebellum,   where  they  end  within  the  anterior  superior  worm. 

The  tractus  spino-ccrcbellaris  ventralis  or  Gowers'  tract  alscj  lies  at  the  periphery 
of  the  lateral  column,  in  front  of  the  direct  cerebellar  tract,   and  likewise  ends  within  the 


l62 


THE    FIBRE-TRACTS. 


cerebellum.  The  fibres  take  their  origin  from  cells,  on  the  same  and  the  opposite  side, 
which  lie  in  the  lateral  part  of  the  posterior  horn  and  in  the  central  field  of  the  gray 
substance.  They  ascend  at  first  with  the  direct  cerebellar  tract,  do  not,  however,  enter 
the  restiform  body,  but  continue  as  far  as  the  pons,  then  enter  the  superior  cerebellar 
peduncle  and  pass  backward  to  the  cerebellum,  where  they  end  within  the  anterior  part 
of  the  superior  worm  (Fig.   74,   fibrae  arciformes). 

The  tradus  spino-olivaris  or  b'iangular  bundle  of  Helweg  is  an  additional  small 
tract,  which  lies  at  the  periphery  of  the  lateral  column,  ventral  to  Gowers'  bundle,  and 
establishes    relations    between    the    spinal    cord    and    the    inferior    olivary    nucleus    in    the 


jnedial  Irnndle 


lateral  bundle 


-Diagram  of  the  tracts  of  the  poste 


medulla  oblongata.  The  source  of  the  fibres  has  not  been  positively  determined.  They 
form,  perhaps,  an  ascending  tract,  arising  within  the  gray  substance  of  the  cord  and 
ending  in  the  olive;  according  to  other  views,  the  bundle  conveys  both  ascending  and 
descending  fibres.  The  entire  area  of  the  lateral  column  included  between  the  foregoing 
tracts  and  the  gray  substance,  belongs  to  the  lateral  ground  bundle  or  fasciculus  lateralis 
proprius.  Within  this  again  appear  numerous  endogenous  fibres,  long  and  short  associ- 
ation fibres,  which  bind  together  various  higher  and  lower  lying  segments  of  the  spinal 
cord.  The  short  fibres  lie  close  to  the  gray  substance  and  form  the  lateral  boiaidary 
zone.  In  addition,  within  the  lateral  ground  bundle  are  found  the  following  sets  of  fibres: 
the  iractus  rubro- spinalis  or  Monakow's  bundle,  whose  fibres  descend  from  the  nucleus 
ruber  of  the  opposite  side  and  lie  within  the  cord  medial  to  the  direct  cerebellar  and 
ventral  to  the  lateral  pyramidal  tract,   partly   within  the   field  of   the  latter.      The  tractus 


PATHS    OF  THE    SPINAL    CORD. 


163 


Goirs  column 


Btirdnch's  column 


vestibulo-spinalis  lateralis,  from  Deiters'  nucleus,  passes  somewhat  more  \'entral.  Medial 
to  Gowers'  bundle  lies  the  tractiis  spino-thalamicus.  The  fibres  of  this  path  are  the 
axones  of  the  commissure- cells  of  the  cord,  which  pass  through  the  anterior  commissure 
to  the  opposite  lateral  column  and  there  turn  upward.  The  termination  of  the  path  is 
in  the  thalamus.  The  tradus  spino-tedalis  consists  of  a  fibre-strand,  that  accompanies  the 
spino-thalamic  tract  and  ends  in  the  region  of  the  corpora  quadrigemina.  The  entire 
path  is,  therefore,  also  called  the  tradus  spino-tedalis  et  thalamicus.  Approximately  within 
the  same  field,  the  tradus  tedo-spinalis  lateralis  descends  from  the  quadrigeminal  region; 
likewise,  in  the  vicinity  of  the  spino-thalamic  fibres,  the  tradus  thalamo-spinalis  descends 
as  a  path  from  the  thalamus. 

3.    TRACTS   OF  THE   POSTERIOR   COLUMN. 

The  posterior  column  is  composed,  in  largest  part,  of  the  continuations  of  the 
sensory  posterior  root-fibres,  that  proceed  from  the  spinal  ganglia  (Fig.  150).  The  cells 
of  the  latter  give  off  a  nerve-process,  which  soon 
divides  into  two  branches,  one  passing  peripheral- 
ward  and  the  other  centralward.  The  centrally 
coursing  branches  enter  the  spinal  cord,  as  the  pos- 
terior root,  as  tw'o  more  or  less  distinct  bundles. 
One  of  these  is  made  up  of  fine  fibres,  lies  lateral 
and  passes  toward  the  substantia  gelatinosa  Ro- 
landi;  the  other  consists  of  coarse  fibres,  lies  medial 
and  passes  toward  the  posterior  column.  The  en- 
trance zone  of  the  lateral  bundle,  between  the  apex 
of  the  posterior  horn  and  the  periphery  of  the  cord, 
is  known  as  Lissauer's  marginal  zone;  that  of  the 
medial  bundle,  to  the  inner  side  of  the  posterior 
horn,  is  called  the  radicular  zo7ie.  Immediately 
upon  entering  the  spinal  cord,  the  fibres  of  both 
bundles  undergo  a  Y-form  branching.  Both  result- 
ing branches  assume  a  longitudinal  direction  and 
during  their  course,  respectively  up  or  down,  give 
oflf  numerous  collaterals  to  the  gray  substance  of  the 
cord.  The  descending  branch  is  the  thinner  and 
ends,  after  a  short  course,  within  the  gray  substance. 
According  to  their  length,  the  ascending  fibres  are 
short,  medium  or  long.  The  short  fibres  pass  into 
the  gray  substance  after  a  very  limited  course;  those 
of  medium  length  proceed  farther  upward,  but  like- 
wise end  within  the  cord  by  bending  over  into  the 
gray  substance;  while  the  long  fibres  ascend  to  the 
medulla  oblongata,  where  they  end  within  the  poste- 
rior column  nuclei,  the  nucleus  gracilis  and  cuneatus. 

The   fibres   entering   the   cord   below  are   dis-  Fic.  isi. — Diagram  illustrating  the  gradual 

I  ,  ,  1      .1  •  1  !•  1  ,  media]  displacement   of   the   long   tracts  of   the 

placed  more  and  more  towards  the  mid-line  by  the      posterior  column. 


164 


THE    FIBRE-TRACTS. 


fibres  entering  at  higher  levels  ;  those  fibres,  therefore,  that  on  entering  the  cord  occupy  the 
lateral  part  of  the  posterior  column, as  they  ascend  soon  collectively  constitute  the  middle  and, 
finally,  the  innermost  part  of  the  column.  Hence,  as  already  noted,  the  posterior  column 
exhibits  in  the  cervical  region  of  the  cord,  a  subdivision  into  the  medial  fasciculus  gracilis 


Tract.   vestibith'Spinalis  lateralis 


Tract,  csrebro  spinalii.    lateralis 


Fig.  152. — The  chief  tracts  descending  to  the  spinal  cord. 


or  Golfs  column  and  the  lateral  fasciculus  cuneatus  or  Burdach' s  column — a  demarcation 
not  emphasized  in  the  lower  part  of  the  cord.  Goll's  column  consists  essentially  of.  fibres 
that  come  from  the  lower  segments  of  the  cord  and  is  nothing  more  than  the  continuation  of 
the  laterally  situated  fibres  of  the  lower  segments,  which  during  their  ascent  have  been  pushed 
toward  the  mid-line  by  the  new  increments  of  fibres  entering  at  higher  levels.      Or,  we  may 


PATHS    OF  THE    SPINAL   CORD. 


165 


say,  in  the  cervical  region  of  the  cord,  Goll's  column  is  composed  of  fibres  which  ascend 
from  the  lower  parts  of  the  cord  and  conveys  sensory  fibres  from  the  lower  extremities 
and  the  lower  half  of  the  trunk,  while  Burdach's  column  carries  sensory  fibres  that  enter 
the  spinal   cord  from   the  upper  half  of  the  trunk  and   the  upper  extremities  (Fig.  151). 


Tract,  sfiiio  tknln. 


Fu;.   1 5.1. — The  chief  tracts 


nding  from  the  spinal  cord. 


The  terminal  arborization  of  the  ascending  fibres  and  of  the  collaterals  occurs  in 
almost  all  parts  of  the  gray  substance  of  the  same  side  of  the  cord  ;  a  small  i)art  of  the 
fibres  passes,  by  way  of  the  posterior  commissure,  to  the  opposite  side  to  end  within  the 
posterior  horn.  The  short  fibres  and  the  collaterals  of  the  lateral  bundle,  in  particular, 
end  within  the  homolateral  posterior  horn  and  also  within  the  central  field  ;  the  main  fibics 


I66  THE    FIBRE-TRACTS. 

and  collaterals  of  the  median  bundle,  which  end  within  the  cord,  arborize  around  the  cells 
of  Clarke's  column,  the  cells  of  the  intermediate  zone  and  the  anterior  horn  cells.  The 
collaterals  from  the  posterior  column,  which  break  up  around  the  anterior  horn  cells, 
constitute  the  7-eJlex  collaterals. 

The  descending  branches  of  the  fibres  of  the  posterior  column,  entering  the  root- 
zone  medial  to  the  posterior  horn,  caudalward  form  a  bundle  that  in  cross-section  appears 
comma-shaped.  The  fibres  of  this  field,  the  comma  bundle  of  Schultze,  after  a  short 
course  enter  the  gray  substance. 

In  addition  to  the  chief  fibres,  within  the  posterior  column  are  others  which  arise 
in  the  posterior  horns  of  the  cord,  as  the  axones  of  association-cells.  They  course  within 
the  ventral  part  of  the  posterior  column  and  in  cross-section  appear  as  the  ventral  field 
(Fig.    149). 

Finally  to  be  noted  are  fibres  that  extend  from  the  cervical  region  as  far  as  the 
conus  terminalis.  In  the  upper  regions,  they  lie  dorsally  at  the  periphery  of  the  poste- 
rior column,  more  within  the  area  of  Goll's  column  ;  farther  below,  they  migrate  toward 
the  septum  posterius  and,  within  the  sacral  region,  in  cross-section  appear  as  a  small 
medial  oval  field.  This  part  has  been  termed  the  oval  bundle  of  the  posterior  column. 
It  corresponds  to  the  bandelette  m^diale  of  Gombault  and  Philippe,  the  dorso-medial 
sacral  field  of  Obersteiner  and  the  tractus  cervico-lumbalis  dorsalis  of  Edinger. 

The  chief  tracts  descending  to  and  ascending  from  the  spinal  cord  are  represented  in 
Figs.  152  and  153. 

THE  MEDULLA  OBLONGATA. 

The  medulla  oblongata  forms  the  transition  from  the  spinal  cord  to  the  brain.  The 
intimate  make-up,  relatively  simple  within  the  spinal  cord,  at  the  same  time  undergoes 
manifold  modifications.  Not  only  does  the  gray  substance  change  its  form,  but  new 
masses,  large  and  small  nuclei,  appear.  Coincidentally,  a  rearrangement  of  certain  systems 
of  the  white  substance  occurs,  certain  tracts  of  fibres  are  suppressed  and  new  ones  make 
their  appearance.  Almost  each  cross-section  presents  a  different  picture.  It  would  carry 
us  too  far  to  follow  accurately  at  this  place  the  structure  of  the  medulla  oblongata  in 
its  topographical  relations,  as  shown  in  transverse  sections.  The  study  of  the  fibre- 
tracts  in  the  brain  and  spinal  cord,  without  the  use  of  serial  sections,  is  impossible ; 
and  especially  the  study  of  the  fibre-tracts  in  the  medulla  oblongata  offers  difficulties 
as  nowhere  else. 

The  reader  is  particularly  referred,  therefore,  to  Part  III  of  this  book,  in  which,  by 
means  of  the  drawings  of  serial  sections,  the  most  important  tracts  may  be  followed 
through  the  entire  brain-stem.  By  means  of  these  microscopical  pictures  and  the  assist- 
ance of  the  following  diagrammatic  figures,  the  reader  will  be  able  to  find  his  way. 

In  the  consideration  of  the  morphology,  the  most  important  gray  masses  of  the 
medulla  oblongata  have  been  mentioned ;  we  may  limit  ourselves,  therefore,  to  the  pres- 
entation of  the  connection  of  these  gray  masses  with  other  parts  of  the  central  nervous 
system.  Then,  as  supplementary,  the  origin  of  the  cerebral  nerves  will  be  more  closely 
considered,  since,  as  pointed  out  in  the  morphological  section,  the  nuclei  of  most  of  the 
cerebral  nerves  are  situated  along  the  floor  of  the  fourth  ventricle. 


PATHS    OF  THE    MEDULLA    OBLONGATA. 


167 


We  proceed  most  advantageously,  if  we  trace  upward  the  fibre-systems  of  the  white 
substance  of  the  cord,  which  were  described  in  the  preceding  section.  At  the  same  time, 
we  will  ignore  the  fibre-systems,  which  come  from  the  brain  and  descend  in  the  cord  and 
have  been  mentioned  repeatedly  in  previous  sections. 

Let  us  first  follow  the  trad  of  the  posterior  column.  The  fibres  of  Burdach's  and 
of  Goll's  column  end  in  the  nuclei  of  the  posterior  column,  that  is,  within  the  nucleus 
fasciculi  cunati  and  the  nucleus  fasciculi  gracilis.  From  these  nuclei  further  tracts  are 
developed,   of    which   one  in   particular,   the   tract   establishing  relations  between  the  pos- 


Lemniscus  medialis 


Tractus  spino-ihala 


Nucl.  funic,  post. 


Fig.  154. — Posterior  column  tract,  medial  fillet  and  tegmental  tract. 


terior  column  nuclei  and  the  thalamus,  now  concerns  us.  The  fibres  pass,  as  the 
axones  of  the  cells  within  the  cuneate  and  gracile  nuclei,  in  ventrally  directed  courses, 
the  fibrae  arcuatae  internae,  toward  the  mid-line,  where  by  decussation  they  form  the 
raphe.  After  crossing,  the  fibres  assemble  close  to  the  mid-line  and,  turning  upward,  pass 
longitudinally  to  higher  levels.  The  field  so  formed  is  known  as  the  interolivary  stratum, 
on  account  of  its  position  between  the  two  inferior  olivary  nuclei.  The  fibre-bundles 
can  be  traced  through  the  pons  and  the  mid-brain  as  far  as  the  thalamus,  where  they 
end  in  the  nucleus  lateralis  and  in  the  centrum  medianum.  This  is  the  path  usually 
called  the  medial  fillet  or  lemniscus  medialis ;  it  is  also  known  as  the  tractus  bulbo- 
thalamicus. 


1 68 


THE    FIBRE-TRACTS. 


Tractus  spino-thalam. 


~  Fasc.  grac.  et  cnneat. 


Fig.  155. — Course  of  the  medial  fillet. 


THE    MEDIAL    FILLET. 


169 


The  medial  fillet  is  not  composed  exclusively  of  fibres  which  come  /rem  the  nuclei 
of  the  posterior  columns.  During  its  course  through  the  medulla  oblongata,  the  fillet-tract 
is  augmented    by  the  fibres  from    the    spinal   cord,  which  we  have  studied  as  the  tractus 


N.  ruber 


Tractus  cerebello-tegutentaUs 


Nuci.  gract'is  et  cnneatus 


atae  int^man t 
continued  a%  Jibrae  arcuatae 
venti  aUt  extertuie 


Pre.  156  — ^Formation  of  the  rcstiform  body, 

spino-thalamicus.  In  addition,  as  will  be  pointed  out  later,  fibres  come  from  the  terminal 
nuclei  of  the  cranial  nerves.  All  these  contributions  collectively  constitute  the  medial 
fillet,  which  ends  within  the  thalamus. 

Still   other  tracts  arise   from  the    posterior  column   nuclei    and    unite  tlie   latter  with 
the  cerebellum.      Some    of   these  fibres    pass,  as    do    the  above-mentioned  fibrae  arcuatiie 


lyo  THE   FIBRE-TRACTS. 

internae,  first  towards  the  mid-line  and  there  cross.  They  course,  however,  not  longitu- 
dinally within  the  interolivary  stratum,  but  pass  ventrally  along  the  raphe  as  far  as  the 
anterior  medial  fissure,  then  around  the  pyramids  and  the  olives  as  the  fibrae  arcuatae 
externae  ventrales,  and  continue  as  constituents  of  the  restiform  bodies  to  the  cerebellum. 
Other  fibres  issue  dorsally  from  the  posterior  column  nuclei  and  pass  directly  to  the 
corpus  restiforme  as  the  fibrae  arcuatae  externae  dorsales  (Fig.  156).  Perhaps  these  are 
joined  by  direct  fibres  from  the  posterior  column  tracts. 

The  constitution  of  the  corpus  restiforme,  or  the  inferior  cerebellar  peduncle,  may 
now  be  considered.  Although  the  tracts  ascending  to  the  cerebellum  from  the  spinal 
cord  and  the  medulla  are  the  principal  factors  in  its  make-up,  additional  paths  of  especial 
importance  are  contributed  to  the  restiform  body  by  the  fibre-bundles  from  the  vestibular 
nerve  and  its  end-nucleus. 

The   restiform    body    consists  of   two  chief  parts,   a  lateral  and  a  medial  division. 

The  lateral  division  is  formed  by  the  following  fibre-bundles: 

a.  The  tradus  spino-cerebellaris  dojsalis  or  direct  cerebellar  tract.  Although  the 
tractus  spino-cerebellaris  ventralis  or  Gowers'  bundle  likewise  passes  to  the  cerebellum,  it 
reaches  the  latter,  not  by  way  of  the  restiform  body,  but,  farther  above,  in  conjunction 
with  the  superior  cerebellar  peduncle  (Figs.   157  and  178). 

b.  The  fibres  from  the  nucleus  gracilis  and  cuneatus  of  the  same  and  of  the  opposite 
side:  fibrae  arcuatae  externae  dorsales  et  ventrales,  as  well  as  direct  fibres  from  the 
posterior  column. 

c.  A  few  fibres  from  the  miclei  arcuati  or  pyramidal  nuclei. 

d.  Fibres  from  the  lateral  column  nuclei. 

e.  Fibres  from  the  inferior  olivary  nucleus. 

The  last  fibres — tractus  olivo-cerebellaris — contribute  the  chief  bulk  of  the  lateral 
division  of  the  peduncle.       They  arise  in  largest  part  from  the  contralateral    olive,   a  few 

fibres    coming    also    from    the    olive  of    the 

lbi7>i  ^ 

same  side,  and   end,  as   do  the   other   fibres 
of    the    lateral    division,    within    the    cortex 

Tractus  sptno-     I  \     I'ractiis  spiyto- 

cereb.  ventralis    1     ...^v^  ^'^^^^3    *''^^^^'  dorsalis  q\    f^g    WOrm 

{Gowers)  \     ^^         /^^^       1       iFleclisig) 

The  medial  division  consists  of  two 
chief  varieties  of  fibres: 

a.  One  set  of  fibres  is  the  sensory 
root-fibres  of  certain  cerebral  nerves,  as  the 
trigeminus    and    the    vestibular,    which    pass 

Fig.    157. —  Schematic    representation    of    the    course    of  ,.         ,      ,         .,  u    11    „J *.;*.. ,*..^   4-l,« 

tv,  V    »  K  11    •  ^^   ,r  ,^A  „»„f,=ii=  direct    to    the    cerebellum    and  constitute  the 

the  tractus  spino-cerebellans  dorsalis  and  ventraUs. 

direct  sensory  cerebellar  ti'act  of  Edinger. 
b.   The  other  fibres  connect  the  nuclei  of  the  sensory  cerebral  nerves  with  the  cere- 
bellum; among    these   connections,  those   of   the   vestibular   nucleus   with    the   cerebellum 
deserve  special  notice. 

The  termination  of  the  fibres  of  both  sets  is,  in  largest  part,  within  the  nucleus 
tegmenti  of  the  cerebellum.  Fibres  pass  also  in  the  opposite  direction  from  the  nucleus 
tegmenti  or  roof  nucleus  to  the  end-nuclei  of  the  sensory  nerves,  Deiters'  and  Bechterew's 


THE    RESTIFORM    BODY.  171 

nuclei  especially  receiving  such  fibres.  These  bundles,  that  bring  the  nuclei  of  the  sensory 
cerebral  nerves  into  relation  with  the  cerebellum,  constitute  the  iradiis  nucleo-cerebellaris. 
The  latter  forms  an  iiidired  sensory  cerebellar  tract,  in  contrast  to  the  above-mentioned 
direct  one.  Fibres  from  the  cerebellum  also  pass  caudally  to  the  medulla  oblongata  by 
way  of  the  restiform  body. 

The  tractus  ccrebello-bidbaris  or  fastigio-bulbaris  is  a  descending  bundle,  which 
proceeds  especially  from  the  nucleus  tecti  of  the  opposite  side  and,  perhaps,  also  from 
the  nucleus  dentatus.  The  bundle  is  known  also  as  the  tractus  uncinatus  (Russel-Thomas). 
The  fibres  pass  above  the  Superior  cerebellar  peduncle  and,  in  their  farther  course,  reach 
the  medial  division  of  the  restiform  body.  Their  termination  is  partly  within  Deiters' 
nucleus  and  partly,  farther  caudalward,  within  certain  nuclei  of  the  medulla  oblongata, 
along  with  collaterals  to  the  motor  nuclei  of  cerebral  nerves — V,  VII  and  X.  Atten- 
tion has  been  called  to  these  paths,  as  the  tractus  cerebello-tegmentaks  biilbi,  when 
considering  the  chief  connections  of  the  cerebellum.  Such  cerebellofugal  tracts  proceed 
from  the  restiform  body,  with  the  fibrae  arcuatae  externae  ventrales,  to  the  olive  and 
the  pyramid  and  ascend  within  the  raphe  to  the  formatio  reticularis  of  the  medulla 
oblongata. 

The  inferior  olivary  nucleus,  as  we  have  seen,  gives  off  a  robust  fibre-bundle,  which 
passes  to  the  corpus  restiforme  of  the  opposite  side  and,  thence,  to  the  cerebellum.  A 
small  number  of  fibres,  on  the  other  hand,  arise  within  the  cerebellar  cortex  and  descend 
to  the  opposite  olive.  The  olivary  nucleus  possesses  still  further  connections.  Thus, 
from  the  ascending  tractus  spino-cerebellares  collaterals  are  sent  to  the  inferior  olivary 
nucleus,  while  other  fibres  are  received  from  the  tractus  spino-olivaris  or  Helweg's  tri- 
angular tract,  as  well  as  from  the  tractus  thalamo-olivaris.  By  means  of  the  last-mentioned 
path,  impulses  from  the  thalamus,  and  also  from  the  cerebral  cortex  by  way  of  the 
thalamus,  are  carried  to  the  inferior  olive  and,  by  way  of  the  olivo-cerebellar  tract,  to  the 
cerebellum  (Fig.    145). 

The  medial  fillet  or  interolivary  stratum  appears  in  cross-sections  of  the  medulla 
as  a  field,  that  lies  between  the  two  olives  at  the  sides  of  the  raphe  (see  Part  III). 
Dorsally,  as  the  apex  of  this  field,  the  posterior  longitudinal  bundle  or  the  fasciculus 
longitudinalis  medialis  is  seen  as  a  small  bundle  of  longitudinally  coursing  fibres.  It  will 
be  considered  more  fully  in  connection  with  the  vestibular  nerve  (page  182).  Lateral  to 
the  interolivary  stratum  and  dorsal  to  the  olive,  a  field  spreads  out  which,  in  addition 
to  numerous  scattered  nerve-cells,  contains  longitudinally  coursing  nerve-fibres.  This 
area,  the  upward  continuation  of  the  formatio  reticularis  of  the  spinal  cord,  is  known 
as  the  association  field  of  the  medulla  oblongata.  The  formatio  reticularis  extends  far 
up  into  the  mid-brain  and  contains  numerous  connecting  paths,  of  longer  or  shorter 
course,  by  which  manifold  relations  are  established  between  certain  nerve-nuclei.  It  is 
probable  that  within  this  formatio  reticularis  run  those  association  fibres  which  unite  the 
nuclei  of  the  vagus,  facial  and  phrenic  nerves  for  coordinated  activity  during  respiration. 
Repeated  mention  has  been  made  of  tracts,  coming  from  other  parts  of  the  brain, 
which  have  their  ending  within  this  formatio  reticularis.  The  reader  should  refer  to 
the  section  on  the  Reflex  Tracts  (page  192),  as  well  as  to  the  microscopical  illustrations 
in  Part  III. 


THE   FIBRE-TRACTS. 


THE  CEREBRAL  NERVES. 

NERVUS    OLFACTORIUS. 

The  first  member  of  the  conventional  series  of  twelve  cranial  nerves,  the  nervus 
olfactorius,  is  represented  by  the  short  peripheral  paths,  the  fila.  olfactoria,  connecting  the 
olfactory  mucous  membrane  with  the  glomeruli  within  the  bulbus  olfactorius.  Since  the 
structures  formerly  described  as  the  first  cerebral  nerve,  the  olfactory  bulb  and  tract,  are 
parts  of  the  rhinencephalon,  their  consideration  falls  properly  with  that  of  the  brain. 
They  have  been  discussed  under  the  Fibre-Paths  of  the  Rhinencephalon  (page  144),  to 
which  the  reader,  therefore,   is  referred. 


NERVUS    OPTICUS. 

The  fibres  of  the  optic  nerve  arise  within  the  retina  and  are  the  axones  of 
the  ganglion  cells  located  within  the  ganglion-cell  layer  of  the  nervous  tunic  of  the  eye. 
They  extend  to  the  chiasm.       Here,   one  part  of  the  fibres  passes  to  the  tractus  opticus 

of  the  opposite  side,  the  other  part  passes 
direct  to  the  tract  of  the  same  side.  The 
fibres  end  within  the  corpus  geniculatum 
laterale,  the  pulvinar  and  the  superior 
coUiculus ;  these  end-stations  constitute 
primary  visual  centres.  From  the  lateral 
geniculate  body  and  the  pulvinar,  fibres 
pass  through  the  hindmost  part  of  the 
posterior  limb  of  the  capsula  interna  to 
the  secondary  or  cortical  visual  ceyitres 
within  the  cortex  of  the  cuneus,  thereby 
forming  the  optic  radiatiofi  of  Gratiolet. 
Fibres  also  pass  in  the  opposite  direction 
from  the  cortical  visual  centre  to  the 
primary  centres.  It  must  be  noted  fur- 
ther, that  fibres  exist,  which  arise  within 
the  primary  centres  and  end  within  the 
retina. 

The  visual  fibres  proper  terminate 
within  the  corpus  geniculatum  laterale 
and  the  pulvinar  thalami  and  probably  do 
not  invade  the  superior  colliculus  of  the  corpus  quadrigeminum,  at  least  in  the  higher 
vertebrates.  The  optic  fibres  which  pass  to  the  superior  colliculus  are  concerned  with  a 
special  duty.  Stimuli  carried  by  these  fibres  to  the  superior  colliculus  are  transferred  to  the 
deeper  lying  oculomotor  nucleus,  resulting  in  the  liberation  of  the  pupillary  reflex.  These 
optic   fibres    ending    in    the   superior  colliculus  are  known,   therefore,   as  pupillary  fibres. 


{Sight  centre) 


Fig.  158. — The  path  of  visual  impuls 


CEREBRAL    NERVES. 


173 


The  pupillary  reflex  consists  in  a  contraction  of  the  pupil  in  response  to  the 
entrance  of  light.  The  reaction  is  e.xhibited  by  both  eyes  ;  that  is,  when  the  light 
falls  on  only  one  eye,  the  contraction  occurs  not  only  in  the  stimulated  eye  (direct 
reaction j,  but  also  in  the  other  eye  (consensual  reaction). 


Fig.  159. — The  course  of  the  visual  path. 

The  intercentral  paths  of  the  puiiillary  reflex  are  not  positively  established,  although 
It  may  be  regarded  as  certain,  that  the  entire  reflex-tract  is  made  up  of  a  sequence 
including  several  neurones.      It  may  be  assumed  that  the  stimulus  passes  : 

a.  From  the  retina  to  the  superior  colliculus  ; 

b.  From  the  superior  colliculus  to  the  nucleus  of  the  oculomotor  nerve ; 

c.  From  the  oculomotor  nucleus  to  the  ciliary  ganglion.; 

d.  From  the  ganglion  ciliare  to  the  sphincter  pupillae  muscle. 

Since  the  illumination  of  one  eye  causes  uniform  contraction  of  both  pupils,  the  re- 
flex being,  therefore,  homo-  and  heterolateral,  it  follows  that  the  impulse  from  one  colliculus 
must  he  transferred  to  both  oculf)motor  nuclei,   or  one  nucleus  must  be  able  to  stimulate 


174 


THE    FIBRE-TRACTS. 


Ganglion 
ciliarc 


both  the  right  and  left  sphincter  pupillae  muscles.  The  particular  fibre-bundle,  by  means  of 
which  the  impulse  is  transferred  from  the  superior  colliculus  to  the  oculomotor  nucleus,  is  not  ■ 
definitely  determined.  In  Fig.  i6o,  the  refie.x  path  is  schematically  represented,  with  the  as- 
sumption, that  the  fibres  proceeding  from  the  superior  colliculus  reach  both  oculomotor  nuclei. 
A  knowledge  of  the  course  of  the  fibres  of  the  optic  nerve,  particularly  their  semi- 
decussation, supplies  the  explanation  of  one  of  the  most  important  disturbances  of  vision — 
hemiopia  (half  seen)  or  hemianopsia  (half  not  seen).  If  the  conduction  of  one  optic  tract, 
for  example  the  left,  be  interrupted  by  a  lesion,  the  stimuli  coming  from  the  left  retinal 
halves  of  the  two  eyes  -can  no  longer  be  transmitted  to  the  cortical  centres  in  the  left 
hemisphere,  the  right  halves  of  the  visual  fields  are  lost  and  only  the  left  halves  of  fixed 
objects  are  still  seen  (Fig.  158).  This  condition  is  spoken  of  as  homolatei-al  or  homony- 
mous hemianopsia  or  hemiopia.  Lesion  of  the  left  tractus  leads  to  right-sided  homonymous 
hemianopsia  or  to  left-sided  hemiopia  ;  lesion  of  the  right  tract  leads  to  left-sided  homonymous 

hemianopsia  or  to  right-sided  hemiopia. 
Homonymous  hemianopsia  follows,  of 
course,  not  only  lesion  of  the  tractus 
opticus,  but  also  lesion  of  the  secondary 
paths  connecting  the  primary  and  sec- 
ondary centres,  that  is  within  the  optic 
radiation,  or  lesion  of  the  cortical  centre. 
In  relation  to  the  diagnosis  of  the  seat 
of  the  lesion,  the  pupillary  reaction  pos- 
sesses a  certain  significance.  If  in  ho- 
monymous hemianopsia  the  light-refle.x 
is  lost  when  the  insensitive  half  of  the 
retina  is  illuminated,  the  seat  of  the  lesion 
is  the  tractus  (Wernicke's  hemianopsic 
pupillary  rigidity  or  hemiopic  pupillary 
'•>  reaction).  If,  on  the  contrary,  the 
light-reflex  of  the  pupil  is  intact,  then 
the  lesion  lies  higher,  for  example,  in 
the  internal  capsule  or  in  the  cerebral  cortex.  In  the  majority  of  cases  of  homonymous  hemian- 
opsia, we  have  to  do  with  tumors  of  the  occipital  lobe,  more  rarely  with  lesions  of  the  tractus 
opticus.  Complications  associated  with  hemianopsia,  such  as  hemiplegia,  hemiparesis,  con- 
tractions and  aphasic  disturbances  (with  right-sided  hemianopsia),  must  also  be  borne  in  mind. 
The  same-sided  or  homonymous  hemianopsia  is  the  opposite  of  the  heteronymous 
hemianopsia,  which  occurs  more  rarely  than  the  homonymous.  When  the  temporal  halves 
of  both  visual  fields  are  wanting,  such  heteronymous  hemianopsia  is  known  as  tetnpoi'al 
hemianopsia.  In  such  cases,  the  lesion  is  situated  within  the  chiasm,  either  in  the  middle 
or  in  the  anterior  or  the  posterior  angle  of  the  chiasm,  whereby  the  decussating  fibres  are 
involved.  Temporal  hemianopsia  is  observed,  for  example,  in  acromegaly,  in  which  the 
enlargement  of  the  hypophysis  cerebri  concurrently  affects  the  chiasm.  When  the  nasal 
halves  of  both  visual  fields  are  wanting,  the  condition  is  spoken  of  as  nasal  hemianopsia 
and  is  produced  by  involvement  of  the  uncrossed  fibres,  as  when  the  chiasm  is  subject  to 
pressure  on  both  sides  in  the  lateral  angle  by  enlarged  carotids. 


N.  oculomotorius 

160. — The  pupillary  reflex  path. 


CEREBRAL    NERVES. 


175 


NERVUS    OCULO.MOTORIUS. 

The  oculomotor  nerve  arises  in  the  nucleus  nervi  ocidomotorii,  which  lies  in  the  region 
of  the  superior  colliculus,  ventral  to  the  aquaeductus  Sylvii,  within  the  floor  of  the  central  gray 
substance  (Figs.  88  and  89).     The  nucleus  consists  of  a  medially  placed  medial  nucleus  and 


-The  deep  origins  of  the  motor 


a  pair  of  large-celled  lateral  nuclei.  The  nerve  conveys  fibres  which  originate  within  the  me- 
dial nucleus  and  the  lateral  nucleus  of  the  same  and,  in  part,  of  the  opposite  side.  The  fibres 
pass  ventrally  in  laterally  convex  curves  and  emerge  from  the  brain-stem  along  the  sulcus  nervi 
oculomotorii  on  the  medial  surface  of  the  pedunculus  cerebri.  The  voluntary  innervation  of 
the  nucleus  proceeds,  as  in  the  case  of  all  the  motor  cere- 

Accomtnodation 

bral  nerves,  from  the  cerebral  cortex.     The  entire  path  of  ;  p„/,iii„ 

conduction  includes: 


a.  The  central  neurone — cerebral  cortex  to  nucleus; 

b.  The    peripheral    neurone  —  nucleus,     peripheral 
nerve,   muscle. 


Levator  paipebrae 
Rectus  bupenor 

Rec(u5inlfrnus 
Obliquus  inferior 
Rectus  inferior 


Fig.  162. — Subsidiary  nuclei  of  the  ocu- 
lomotor nucleus.     iBernheimer.) 


It  must  be  pointed  out,  however,  that  the  course  of 
the  central  path  is  not  yet  known;  probably  the  path  is 
composed  of  several  neurones.  Likewise,  uncertainty  exists 
regarding  the  location  of  the  cortical  centres,  which  have  been 
variously  assumed  as  lying  within  the  gyrus  angularis,  the 

occipital  lobe  or  the  frontal  lobe.  The  centre  for  voluntary  eye-movements,  however,  is  quite 
generally  regarded  as  including  the  posterior  part  of  the  second  or  middle  frontal  convolution. 
Investigations  have  shown,  that  the  entire  oculomotor  nucleus  is  made  up  of  certain  groups  of 
cells,  of  which  a  particular  group  always  gives  origin  to  the  fibres  for  d  particular  muscle.  Con- 
cerning these  special  subdivisions  of  the  nucleus,  however,  we  shall  not  enter  more  fully,  for 
the  rc-a.son  that  these  relations,  as  yet,  have  been  by  no  means  definitely  established.    Fig.  162 


176 


THE    FIBRE-TRACTS. 


represents  the  individual  cell-groups,  according  to  the  investigations  of  Bernheimer  on 
monkeys.  In  the  middle  is  the  medial  chief  nucleus,  on  either  side  the  lateral  chief  nucleus 
vi-ith  its  various  subdivisions,  and,  medial  from  the  latter,  the  small  lateral  nucleus,  which 
is  also  known  as  the  nucleus  of  Editiger-  Westphal. 

NERVU5    TROCHLEARIS. 

The  trochlear  nerve  has  its  origin  in  the  nucleus  tiey-vi  trochlearis,  which  is  located 
in  the  caudal  prolongation  of  the  oculomotor  nucleus  in  the  region  of  the  inferior  colliculus. 
The  fibres  of  the  fourth  nerve  pass  dorsally,  cross  in  the  velum  medullare  anterius  and 
emerge  from  the  brain-stem  behind  the  quadrigeminal  bodies,  on  either  side  of  the  frenu- 
lum veli  medullaris  anterioris.      As  in  the  case  of  the  oculomotor  nervi,  the  path  includes: 

a.  The  central  jieurone — from  cerebral  cortex  to  nucleus; 

b.  The  peripheral  neurone — nucleus,   peripheral  nerve,   muscle. 

NERVUS    ABDUCENS. 

The  nucleus  of  the  abducens  nerve  lies  in  the  floor  of  the  fourth  ventricle  and  in 
the  colliculus  facialis.  The  emergent  fibres  of  the  sixth  nerve  pass  ventrally  and  leave 
the  brain-stem  at  the  posterior  border  of  the  pons.      The  path  includes: 

a.  The  central  neicrone — from  cerebral  cortex  to  nucleus; 

b.  The  peripheral  neurone — nucleus,    peripheral  nerve,   muscle. 


NERVUS   TRIGEMINUS. 

Here  a  motor  part  and  a  sensory  part  are  to  be  distinguished  (Figs.  163  and   164). 

I.    Motor  Portion.     The  central  neuronic  takes  origin  in  the  cerebral  cortex  of  the 

lower   third  of    the  central    convolutions,   passes  with  the  pyramidal   tracts  downward  and 

NitcUits  radicis  descendentis  N.  trtgeiiihit 

,'  Motor  nucleus  n.  trigetn, 

^'Sensory  mtcleiis  n,  trigem. 

Dorsal  motor  vagits 

Sensory  nucleus  vago- 
^  lossopharyttgeiiS 


Fig.  163. — Course  of  the  trigeminus,  va^s  and  glossopharyngeus  within  the  brain-stem. 


CEREBRAL   NERVES. 


177 


ends  in  the  chief  motor  7nicleus,  within  the  dorso-lateral  part  of  the  tegmentum  of  the 
pons.  The  peripheral  neurone  arises  within  this  motor  nucleus,  the  motor  root  of  the 
ner\'e  receiving  also  fibres  from  the  nucleus  of  the  opposite  side.  The  fibres  emerge  from 
the  pons  as  the  poriio  vmtor  nervi  trigenmii  and  pass  to  the  muscles.  A  small  part  of 
the  motor  root  arises  from  small  cells,  which  lie  lateral  to  the  Sylvian  aqueduct  within 
the    region  of    the    corpora   quadrigemina  and  constitute  the    nucleus    radicis   descendentis 


Sensory  terminnl  nucleus 


D''sce*ieii}ig  sensory  trigeminal 

root  and  its  ending  in  sensory 

nucleus 


of  the  root-fibres  of  the  triKeti 


neri'i  Irigemini.  This  group  of  cells  joins  caudally  the  cell-area  of  the  locus  caerulus. 
The  fibres  arising  from  these  cells,  after  giving  off  collaterals  to  the  chief  motor  nucleus, 
pass  outward  with  the  other  peripherally  directed  processes  of  the  motor  neurones. 

2.  Sensory  Portion.  The  origin  of  the  sensory  part  of  the  trifacial  nerv^  lies 
within  the  ganglion  Gasseri.  The  axones  of  the  unipolar  ganglion  cells  of  this  ganglion 
divide  into  two  branches.  One  of  these  extends  peripherally  as  the  peripheral  nerve, 
the  other  passes  centrally,  enters  the  pons  as  the  portio  major  nervi  Irigemini,  and  runs 
to  the  sensory  end-nucleus  of    the    trigeminus,   close  to    the    motor    nucleus.      Here  each 


178  THE   FIBRE-TRACTS. 

fibre  divides  into  an  ascending  and  a  descending  branch.  The  ascending  branch  ends 
within  the  sensory  nucleus  within  the  pontile  tegmentum.  The  descending  branch  ends, 
after  giving  off  numerous  collaterals,  in  a  nucleus  that  is  nothing  more  than  the  caudal 
prolongation  of  the  sensory  nucleus.  The  descending  branches  form  collectively  the 
tradus  spinalis  7iervi  trigemini;  the  gray  substance  in  which  this  path  ends,  constitutes 
the  nicclens  tradus  nervi  trigemini.  The  descending  tract,  as  well  as  the  nucleus,  can 
be  followed  downward  as  far  as  the  cervical  cord,  the  nucleus  being  identical  with  the 
substantia  gelatinosa  Rolandi  capping  the  posterior  horn.  From  the  sensory  end-nucleus 
arises  the  //  neurone.  The  fibres  pass  towards  the  mid-line,  giving  off  collaterals  to  the 
nucleus  of  the  facial  nerve,  cross  to  the  fillet-tract  of  the  opposite  side,  there  turn  upward 
and  run  forward  (partly  within  the  medial  fillet  and  partly  as  a  more  laterally  placed 
special  ascending  bundle),  and  later  enter  the  thalamus  with  the  medial  fillet.  Finally, 
a  ///  neuroyie  succeeds  the  second  one,  thus  linking  the  thalamus  with  the  cortical  sensory 
area.  Still  to  be  mentioned  are  sensory  fibres,  which  pass  direct  to  the  cerebellum  as 
constituents  of  the  direct  sensory  cerebellar  tract;  further,  fibres  which  pass  from  the 
sensory  end-nucleus  to  the  cerebellum  as  constituents  of  the  tractus  nucleo-cerebellaris. 

NERVUS    FACIALIS   AND    NERVUS    INTERMEDIUS    WRISBERGI. 

The  facial  nerve  arises  in  the  nudeus  nervi  facialis,  which  lies  within  the  ventral 
area  of  the  pontile  tegmentum,  ventro-lateral  to  the  abducent  nucleus.  The  fibres  spring- 
ing from  the  nucleus  first  proceed  dorsally,  pass  around  the  nucleus  of  the  abducent 
nerve — the  facial  knee  and  the  colliculus  facialis — then  course  ventrally  and  emerge 
from  the  brain-stem  at  the  posterior  border  of  the  pons,  lateral  to  the  olive.  The  volun- 
tary innervation  of  the  nucleus  is  effected  by  fibres,  which  start  from  the  lower  third  of 
the  precentral  convolution,  pass  through  the  internal  capsule  (knee),  then  through  the 
cerebral  peduncle  to  the  pons,  and,  finally,  to  the  homo-  and  the  contralateral  facial 
nucleus.     The  path  includes,   as  in  the  case  of  the  other  motor  nerves: 

a.  The  central  neurone — from  cerebral  cortex  to  nucleus; 

b.  The  peripheral  neurone — nucleus,   peripheral  nerve,   muscle. 

The  facial  tmcleus  resembles  the  oculomotor  nucleus  in  including  a  number  of 
different  groups  of  cells,  in  which,  in  the  first  place,  we  distinguish  two  chief  groups,  an 
upper  and  a  lower  facial  nucleus.  The  upper  contains  cells,  whose  axones  form  collec- 
tively the  superior  facial  branch;  the  lower,  cells  whose  axones  form  the  inferior  facial 
branch.  Moreover,  the  superior  facial  nucleus  receives  its  innervation  from  the  motor 
centres  of  both  hemispheres,  a  fact  of  clinical  significance.  This  bilateral  innervation 
explains  why,  in  central  facial  paralysis,  the  muscles  supplied  by  the  upper  facial  division 
are  not  involved  in  the  paralysis,  since  innervation  is  still  provided  by  the  unaffected 
central  neurones  of  the  other  hemisphere.  In  peripheral  facial  palsy,  on  the  contrary, 
all  the  muscles  supplied  by  both  the  upper  and  lower  facial  are  paralyzed. 

The  nervus  intermedius  Wrisbergi  (the  nerve  of  Sapolini,  by  whom  it  was 
regarded  as  the  thirteenth  cerebral  nerve)  is  a  mixed  nerve,  which  accompanies  the 
facial  and  continues  as  the  chorda  tympani.  The  motor  fibres  take  origin  in  a  small  cell- 
group  lying  dorso-medial  to  the  facial  nucleus .  The  sensory  fibres  arise  within  the  gan- 
glion geniculi.      The  axones  arising  from  the  cells  of  this  ganglion  divide  into  two  branches. 


CEREBRAL    NERVES. 


179 


One  of  these  passes  peripherally  and  forms,  after  joining  the  motor  fibres,  the  peripheral  nervus 
interniedius,  that  continues  as  the  chorda  tympani.  The  other  branch  passes  centrally, 
enters  the  brain-stem  and  ends  within  the  nucleus  tracbis  solitarii  as  part  of  the  gustatory 
path   (page   189). 

NERVUS    ACUSTICUS. 
The  acoustic  nerve  consists  of  two  parts,  the  nervus  cochleae  and  the  ner\'us  vestibuli. 


I.    NERVUS   COCHLEAE. 

This  nerve  takes  origin  within  the  ganglion  spirale  cochleae.  The  peripherally 
directed  fibres  of  these  bipolar  ganglion  cells  run  to  the  auditory  cells  within  the  organ 
of  Corti;  the  centrally  directed  fibres  enter  the  brain-stem  and  end  in  two  nuclei.  The 
latter  are  the  nucleus  venfralis  nervi  cochleae,  situated  ventral  and  lateral  to  the  corpus 
restiforme,  and  the  nucleus  dorsalis  nervi  cochleae,  or  tuberculum  acusticum,  which  lies 
dorsally,  although  connected  with 
the  ventral  nucleus.  The  impulses 
carried  by  these  peripheral  neu- 
rones are  conveyed  to  the  higher 
levels  by  the  central  path  including: 

a.  Neurones  passing  from  the 
nucleus  ventralis  to  the  mid-line, 
forming  the  corpus  trapezoides.  The 
path  is  augmented  by  fibres  from  the 
superior  olive  and  from  the  nucleus 
of  the  corpus  trapezoides.  After 
crossingthe  mid-line, some  fibres  end 
within  the  superior  olivary  nucleus, 
while  others  are  joined  by  fibres  from 
the  nucleus  of  the  corpus  trapezoides 
and  from  the  superior  olive  of  the 
side  on  which  the  path  now  runs. 

The     fibres     form    collectively  Fig.  i6s.— The  auditory  path. 

the  lateral  fillet  or  lemniscus  later- 
alis, which  ends  within  the  corpus  geniculatum   mediale  and,   chiefly  by  collaterals,  within 
the  inferior  colliculus.      Some  fibres  extend  as  far  as  the  superior  colliculus.      The  lateral 
fillet  recdves  additional    fibres    from  a   grovip    of    cells    lying    in    the    midst   of    tlic   tract, 
known  as  the  nucleus  lemnisci  lateralis. 

b.  Neurones  passing  from  the  nucleus  dorsalis  or  tuberculum  acusticum  <)\er  the 
corpus  restiforme  and,  as  the  superficial  iVr/ac  acusticae,  toward  the  mid-line;  thence  cours- 
ing deeply  to  cross  the  raphe  and  reach  the  opposite  superior  olive,  they  join  the  lateral 
fillet  and  finally  end  within  the  corpus  geniculatum  mediale. 

c.  Neurones  arising  within  the  lateral  geniculate  body  and  ]jassing  to  the  auditory 
centre  within  the  corte.x  of  the  gyrus  temporalis  superior.  Fibres  also  run  in  the  opijosite 
direction,  from  the  auditory  centre  to  the  medial  geniculate  body  and  to  the  inferior 
colliculus. 


i8o 


THE    FIBRE-TRACTS. 


N.cochlea& 


Fig.  i66. — Course  followed  by  the  auditory  impulses. 


CEREBRAL    NERVES. 


i8i 


2.    NERVUS   VESTIBULI. 

The  vestibular  division  of  the  auditory  nerve  arises  within  the  ganglion  vestibulare 
or  Scarpa's  ganglion,  located  at  the  bottom  of  the  internal  auditory  canal.  The  periph- 
erally directed  processes  or  fibres  of  these  ganglion  cells  run  to  the  ampullae,  the 
utricle  and  saccule  of  the  internal  ear;  the  centrally  directed  fibres  enter  the  brain-stem 
and  divide  into  ascending  and  descending  branches.  The  descending  branches  form  a 
descending  vestibular  root  and  end  within  the  nucleus  nervi  vestibularis  spinalis,  which 
extends  as  far  as  the  posterior  column  nuclei.  The  ascending  branches  end  within  the 
nucleus  medialis,  as  well  as  within  the  lateral  Deiters'  nucleus  and  the  upper  Bechterew'  s 
nucleus.  From  these  end-nuclei,  fibres  pass  to  the  cerebellar  worm  as  constituents  of  the 
tractus  nucleo-cerebellaris.      A  part  of   the  vestibular  fibres  pass  direct  to  the  roof-nucleus 


Nucleus  Bechterew 


Nucleus  Deiters 
Nucleus  vestiduii 


Nucleus  tnedialis 
Fig.   167. — Path  of  the  impulses  from 


of  the  cerebellum  as  constituents  of  the  direct  sensory  cerebellar  tract,  the  fibres  giving 
off  collaterals  to  Deiters'  nucleus.  The  medial  nucleus  is  brought  into  relation  with  the 
superior  olive  by  means  of  fibres.  Perhaps  fibres  pass  also  to  the  formatio  reticularis  and 
to  the  thalamus. 

In  view  of  its  importance,  the  system  of  Deiters'  nucleus  claims  closer  attention. 
This  nucleus  receives,  on  the  one  hand,  fibres  from  the  roof-nucleus  of  the  cerebellum  ; 
on  the  other  hand,  as  we  have  seen,  Deiters'  nucleus  gives  origin  to  a  fibre-bundle  that, 
as  the  tractus  vestibulo-spinalis,  passes  to  the  spinal  cord. 

Within  the  same  nucleus,  moreover,  also  another  path,  the  posterior  longitudinal 
bundle  or  the  fasciculus  longitudinalis  medialis,  takes  its  origin.  The  fibres  pass  from 
Deiters'  nucleus  toward  the  mid-line,  some  crossing  the  latter  and  then  dividing  into 
ascending  and  descending  branches.  The  ascending  branches  can  be  followed  upward  as 
far  as  the  oculomotor  nucleus  ;  the  descending  branches  pass  to  the  anterior  column  of  the 


THE    FIBRE-TRACTS. 


spinal  cord.  The  posterior  longitudinal  bundle,  however,  does  not  consist  exclusively  of 
fibres  from  Deiters'  nucleus.  Other  fibres  take  origin  in  the  common  nucleus  of  the 
commissura  posterior  a?id  of  the  fasciculus  longitudinalis  medialis  within  the  forepart  of 


Fasc.  long,  medial. 


Fig.   i68. — Origin  and  course  of  the  post 


'  :  Tract  vestibnlo-sphialis 


longitudinal  bundle. 


the  mid-brain,  in  front  of  the  oculomotor  nucleus.  The  posterior  longitudinal  bundle  may 
be  traced  from  its  nucleus  through  the  mid-brain,  the  pons  and  the  medulla  oblongata 
into  the  spinal  cord,  during  its  course  giving  off  numerous  collaterals  to  the  nuclei  of  the: 


CEREBRAL    NERVES. 


183 


nerves  supplying  the  ocular  muscles.  This  bundle  is  of  great  importance.  It  establishes 
relations  of  the  nuclei  of  the  eye-muscles  to  one  another,  among  which  that  of  the 
abducens  to  the  oculomotorius  nucleus  deserves  particular  attention.  Of  especial  impor- 
tance is  the  connection  of  the  abducent  nucleus  with  those  cells  of  the  oculomotor  nucleus, 
from  which    pass    the  fibres  for    the    rectus    internus,   since    the    synergic  function    of    the 


Nucl.  fasc.  long. 


Fig.  169. — Course  of  the  auditory  path.    Connection  of  Ine  superior  olive  with  the  nucleus  of  the  abducens  {VI)  and,  by  means 
of  the  posterior  longitudinal  bundle,  with  the  nuclei  of  the  other  nerves  (///.  IV)  to  the  ocular  muscles. 


rectus  e.xternus  and  internus,  which  consists  in  the  conjugate  deflection  of  the  eyes  toward 
one  side,  can  be  explained  only  by  the  existence  of  a  direct  or  an  indirect  connection 
Ijetween  these  nuclei.  Fig.  168  represents  the  manner  in  which  the  coordinate  action  of 
the  two  muscles  may  be  explained  upon  an  anatomical  basis.  Connection  of  the  abducens 
nucleus  with  that  of  the  oculomotorius,  by  means  of  the  posterior  longitudinal  bundle,  is 


184  THE    FIBRE-TRACTS. 

positively  established.  Further,  that  the  nerve-fibres  for  the  rectus  internus  arise,  in 
greater  part,  from  the  cells  of  the  oculomotor  nucleus  of  the  opposite  side.  On  the  other 
hand,  it  is  still  undecided,  whether  the  efferent  paths  from  the  cortical  centre  for  synergic 
eye-movements  are  first  interrupted  in  a  special  centre  within  the  quadrigeminal  region, 
or  pass  directly  into  the  posterior  longitudinal  bundle.  In  any  event,  this  tract  undergoes 
a  total  or  partial  decussation  before  it  enters  the  posterior  longitudinal  bundle.  In  Fig. 
1 68,  the  path  from  the  cortex  to  the  nucleus  of  the  bundle  is  represented  as  crossed. 
In  tnis  way,  the  explanation  for  the  following  phenomena  is  supplied.  When  a  cortical 
centre  for  eye-movements  is  stimulated,  the  left  one  for  example,  deviation  of  both  eyes 
toward  the  right  occurs.  On  the  other  hand,  in  left-sided  disease  of  the  cerebral  cortex, 
followed  by  paralysis  of  the  right  half  of  the  body,  deflection  of  both  eyes  toward  the 
side  of  the  lesion,  that  is  the  left,  is  frequently  observed,  since,  under  these  conditions, 
the  eye-muscle  nerves  of  the  left  side  functionally  predominate.  "  In  lesions  of  the  hemi- 
spheres, if  there  is  conjugate  deviation  of  the  eyes,  the  patient  looks  toward  the  injured 
hemisphere  when  there  is  paralysis,  or  the  limbs  are  contorted  during  a  convulsion" 
(Grasset).  The  diagram  explains,  further,  the  deviation  of  the  eyes,  toward  the  side 
opposite  to  the  seat  of  the  lesion,  frequently  observed  in  diseases  of  the  pons.  For 
example,  if  a  lesion  of  the  posterior  longitudinal  bundle  lies  in  the  vicinity  of  the  right 
abducens  nucleus,  deviation  of  the  eyes  toward  the  right  occurs  in  consequence  of  the 
mastery  by  the  nerves  controlling  the  left  eye-muscles. 

The  posterior  longitudinal  bundle  possesses  further  importance,  since  it  brings  the 
vestibular  apparatus  and  the  cerebellum  into  relation  with  the  nuclei  of  the  eye-muscles 
and  the  spinal  cord,  by  means  of  the  fibres  arising  within  Deiters'  nucleus.  It  unites, 
therefore,  the  centres  concerned  in  maintaining  equilibrium  and  orientation  in  space. 

It  is  to  be  noted,  that,  since  a  connection  between  the  superior  olive  and  the 
abducens  nucleus  exists,  relations  of  the  acoustic  nerve,  that  is  of  the  auditory  path,  with 
the  abducens,  and,  by  means  of  the  posterior  longitudinal  bundle,  with  the  other  nuclei 
of  the  eye-muscle  nerves  may  also  be  established.  These  connections  explain  the  occur- 
rence of  reflex  ocular  movements  in  response  to  auditory  impressions  (Fig.    i6g). 

NERVUS  GLOSSOPHARYNGEUS  AND  VAGUS. 

I.  Motor  Portion.  The  efferent  fibres  arise  partly  within  the  nucleus  motorizis 
dorsalis  nervi  vagi  et  glossopharyngei,  which  lies  in  the  floor  of  the  fourth  ventricle 
lateral  to  the  hypoglossal  nucleus  and  medial  to  the  nucleus  alae  cinereae  ;  the  larger 
part  of  the  fibres,  however,  arises  from  the  cells  of  the  7iudeus  vetitralis  or  ambiguus, 
which  lies  within  the  formatio  reticularis  dorsal  to  the  dorsal  accessory  olive.  Since  the 
voluntary  innervation  of  the  nucleus  proceeds  from  the  cerebral  cortex,  the  path  includes  : 

a.  The  central  neurone — from  the  cerebral  cortex  to  nucleus; 

b.  The  peripheral  neurone — nucleus,   peripheral  nerve,   muscle. 

The  root-bundles  passing  out  from  the  dorsal  nucleus  are  the  equivalents  of  motor 
preganghonic  sympathetic  fibres  destined  for  the  innervation  of  involuntary  muscle  ;  this 
nucleus,  therefore,  is  also  designated  as  the  sympathetic  motor  nucleus.  The  fibres  pro- 
ceeding from  the  nucleus  ambiguus,  on  the  contrary,  are  for  the  voluntary  muscle  ;  this 
nucleus,  therefore,   is  known  as  the  somatic  motor  nucleus.      The  latter  consists  of  several 


CEREBRAL    NERVES. 


185 


groups  of  nerve-cells,  the  individual  groups  representing  centres  for  the  particular  groups 
of  muscles  innervated  by  the  vagus.  The  positions  of  these  centres  within  the  nucleus, 
however,  are  not  yet  sufficiently  determined. 

2.  Sensory  Portion.  The  efferent  fibres  arise  within  the  ganglion  supcrius  et 
petrosum  nervi  glossopharyngei  and  ganglion  jugulare  et  nodosum  nervi  vagi  respectively. 
The  peripherally  directed  branches  form  the  peripheral  sensory  nerves  ;  the  centrally 
directed  branches  enter  the  brain-stem  as  the  sensory  root-fibres  and  pass  to  the  end- 
nuclei.      One  part  of  the  fibres  ends  within  the  nucleus  alae  cinereae,   while  another  part 


AIn  cinerea     Trigofnim  hypogtossi 


Fig.  170. — Transverse  section  of  the  medulla  ob- 
longata. Origin  of  the  IX  and  X  (motor  part)  and  of 
the  XII  nerve. 


Fig.  171.— Origin  of  th=  IX  and  X 


forms  a  descending  root,  the  tractus  solitarius,  and  ends  within  the  accompanying  tract  of  gray 
substance,  the  nucleus  tractus  solitarii.  The  central  neurones  arise  within  the  end-nuclei. 
The  fibres  emerging  from  the  end-nuclei  pass  toward  the  mid-line  and  the  interolivary  layer, 
thence  with  the  medial  fillet  to  the  thalamus.  Within  the  latter,  the  third  neurone  takes 
origin  and  ends  within  the  cerebral  cortex.  The  sensory  end-nuclei  are  also  connected  with 
the  cerebellum,  by  means  of  the  tractus  nucleo-cerebellaris.  Further,  all  of  the  centrally 
coursing  sensory  root-fibres  do  not  terminate  within  the  end-nuclei  of  the  glossopharyngeus 
and  vagus,  since  some  of  them  join  the  descending  tractus  spinalis  of  the  trigeminus  nerve. 


NERVUS   ACCESSORIUS. 

The  spinal  accessory  nerve  presents  a  cerebral  and  a  spinal  portion.  The  fibres  of  the 
cerebral  part  arise  from  a  nucleus,  situated  within  the  caudal  prolongation  of  the  nucleus 
ambiguus  ;  further,  from  a  small  dorsal  nucleus,  which  represents  the  caudal  prolongation  of  the 
dorsal  motor  vagus  nucleus.  The  fibres  of  the  spinal  portion  of  the  accessorius  take  origin 
from  cells  situated  in  the  base  of  the  lateral  horn  and  in  the  dorsolateral  part  of  the  anterior 
horn  of  the  spinal  cord,  as  far  down  as  the  fifth,  or  even  seventh,  cervical  segment  of  the  cord. 

The  path  includes: 

a.  The  central  neurone — from  cerebral  cortex  to  the  nucleus; 

b.  The  peripheral  neurone — nucleus,  peripheral  nerve,   muscle. 

As  well  known,  the  accessorius  supplies  the  sterno-cleido-mastoideus  and  trapezius 
muscles.  These  fibres  include  the  spinal  portion  of  the  nerve  and  constitute  the  ramus 
externus,  while  the  fibres  of  the  cerebral  portion,  as  the  ramus  internus,  pass  to  tht- 
vagus,  as  a  part  of  which  they  are  to  be  regarded. 


i86  THE    FIBRE-TRACTS. 


NERVUS    HYPOGLOSSUS. 


The  nucleus  of  the  hypoglossal  nerve  lies  in  the  floor  of  the  fourth  ventricle,  within  the 
trigomim  nervi  hypoglossi.  The  efferent  fibres  pass  from  the  nucleus,  proceed  ventrally  and 
emerge  from  the  brain-stem  between  the  pyramid  and  the  olivary  eminence.    The  path  includes: 

a.  The  central  netcrone — from  cerebral  cortex  (lower  third  of  the  precentral  convolu- 
tion), knee  of  internal  capsule,   nucleus. 

b.  The  peripheral  neurone — nucleus,   peripheral  nerve,   muscle. 

SUMMARY  OF  THE  CHIEF  TRACTS. 

A.    PROJECTION    TRACTS. 

The  entire  sensory  projection  path  from  the  sense-surfaces  (skin,  retina,  labyrinth,  etc. ) 
to  the  sensory  region  of  the  cerebral  cortex,  as  well  as  the  entire  motor  projection  path  from 
the  motor  region  of  the  cerebral  cortex  to  the  muscles,  is  made  up  of  several  paths  of  conduc- 
tion or  projection  systems. 

I.    CENTRIPETAL    TRACTS. 

I.  Ascending  sensory  tracts  from  the  spinal  cord. 

a.  The  path  for  the  conduction  of  impulses  of  touch,  temperature  and  paiii  from 
the  trunk  and  the  extremities. 

Neurone  I:  The  impulse  is  conveyed  from  the  periphery  to  the  ganglion-cells 
within  the  spinal  ganglion  and  thence  to  the  spinal  cord  by  the  posterior  roots.  The 
latter  enter  the  spinal  cord  and  end  within  the  gray  substance. 

Neia-one  II:  Origin  within  the  gray  substance  of  the  spinal  cord.  The  fibres 
pass,  as  the  axones  of  commissure-cells,  by  way  of  the  anterior  gray  commissure  to  the 
opposite  lateral  column  and  form  the  tractus  spino-thalamicus,  which  higher^  up  joins  the 
medial  fillet  and  with  it  ends  within  the  thalamus. 

Neurone  III:  Origin  within  the  thalamus.  Course  to  the  cerebral  cortex,  in  part 
direct  by  way  of  the  internal  capsule,  and  in  part  after  traversing  the  lenticular  nucleus. 
Cortical  ending  within  the  area  of  somatic  sensibility. 

The  conduction  of  impulses  of  contact  or  tactile  sensibihty  is  not  limited  to  the 
spino-thalamic  tract,  but  takes  place  also  through  the  long  tracts  of  the  posterior  columns. 

b.  The  path  for  the  conduction  of  the  muscle-sense  from  the  trunk  and  the  extremities. 
Neurone  I :     The  impulse  is  conveyed,  as  in  the  case  of  those  of  touch,  temperature  and 

pain,  first  to  the  spinal  cord.  The  fibres  enter  as  posterior  roots,  do  not,  however,  end  within 
the  gray  substance  of  the  spinal  cord,  but  ascend  within  the  posterior  column  to  the  medulla 
oblongata,  where   they   first  find    their   ending   within  the   nucleus   gracilis  and  cuneatus. 

Neurone  II:  Origin  within  the  posterior  column  nuclei;  course,  after  decussation, 
as  medial  fillet  to  thalamus  and  there  end. 

Neurone  III :     Origin  within  the  thalamus.     Course  to  cortical  somatic  sensory  area. 

The  conduction  of  muscle-sense  is  not  only  by  way  of  the  posterior  column  nuclei  and  the 
medial  fillet,  but  also  shares  the  tracts  passing  to  the  cortex  by  way  of  the  cerebellum,  that  is  by 


CENTRIPETAL  PATHS. 


187 


the  tractus  spino-cerebellaris  ventralis  et  dorsalis.  From  the  cerebellum,  the  conduction  passes 
through  the  superior  cerebellar  peduncle  to  the  thalamus  and  thence  to  the  cerebral  cortex. 
It  is  to  be  noted,  that  tracts  lead  to  the  cerebellum  also  from  the  posterior  column  nuclei. 

The  partly  uncrossed  (muscle-sense  or  deep  sensibility)  and  partly  crossed  (pain 
and  temperature)  conduction  of  sensibility  within  the  spinal  cord,  explains  the  peculiar 
disturbances  of  sensibility  in  hemilesions  of  the  cord,  as  manifested  in  the  Brown-Sequard 
symptom-complex.      In  hemilateral    lesions  of    the  spinal  cord,   we  find,   on  the  same  side 


Tractits  spino-thalam, 


Nuc   grac    et  cuneal. 


-The  sensory  tract. 


as  the  lesion,  paralysis  in  consequence  of  interruption  of  the  descending  motor  paths, 
and  disturbances  of  the  deep  sensibility  or  muscle-sense  in  consequence  of  the  involvement 
of  the  ascending  paths  of  the  posterior  column  and  of  the  spino-cerebellar  tracts  ;  while, 
on  the  side  opposite  the  lesion,  are  found  disturbances  of  superficial  sensibility,  pain  and 
temperature  impulses  in  consequence  of  the  crossed  path  of  the  tractus  spino-thalamicus. 
F"urther,  the  fact  that  the  conduction  of  sensibility,  especially  of  muscle-sense,  also 
takes  place  by  way  of  the  cerebellum,  supplies  the  explanation  of  those  pathological  dis- 
turbances, which  we  designate  as  ataxia  or  errors  of  coordination,  since  the  impulses 
proceeding  from  the  muscles  and  articulations  are  no  longer  transmitted  to  the  cerebellum 
in  consequence  of  the  lesion  of   the  posterior  column  tracts. 


THE    FIBRE-TRACTS. 


2.  Sensory  Tracts  of  the  Cerebral  Nerves. 

a.  The  path  for  the  impulses  of  tmtch,  temperature  and  pain  from  the  integument 
of  the  head  (with  the  exception  of  the  occipital  region  and  certain  areas  of  the  external 
ear — supplied  respectively  by  the  occipital  and  great  auricular  nerves),  further,  from  the 
conjunctiva,  the  mucous  membranes  of  the  nasal  fossae,  of  the  mouth  and  tongue,  of  the 
palate,   of  the  pharynx,   etc.,   lies  in  the  trigeminus,   the  glossopharyngeus,   or  the  vagus. 

b.  The  path  for  the  impulses  of  orientation  and  movement — -7nuscle-setise — from  the 
face  lies  probably  in  the  trigeminus;  that  from  the  larynx  probably  in  the  vagus. 

"^ '" Posterior  coliitnn  tracts 


Reflex  fa^ 


173- — Ascending  tracts  from  the  spinal  cord, 
pain  and  temperature; 


onduction    of    musci 
onduction  of  tactile 


The  impulse  is  carried  from  the  periphery  to  the  ganglion  of  the  corresponding 
nerve,  and  thence  to  the  end-nucleus  within  the  brain-stem.  To  the  peripheral  neurone  I 
is  added  the  central  neurone  II.  The  latter  arises  within  the  sensory  end-nucleus,  its 
axone,  the  efferent  nerve-fibre,  passes  upward  with  the  medial  fillet  and  ends  within  the 
thalamus.     From  here  the  neurone  III  extends  to  the  cerebral  cortex. 

c.  The  path  for  the  visceral  impulses,  from  the  lungs,  heart,  cesophagus, 
stomach,   etc.,  lies  in  the  vagus  and  the  sympathetic. 

d.  The  path  for  the  equilibrium  impulses  lies  in  the  vestibular  nerve,  supple- 
mented by  spinal  fibres.  The  path  leads  to  the  cerebellum,  thence  by  way  of  the  superior 
cerebellar  peduncle  to  the  nucleus  ruber  and  the  thalamus,  and  then  to  the  cerebral  cortex. 


CENTRIPETAL    PATHS. 


189 


e.  The  path  for  the  taste  impulses  lies  in  the  glossopharyngeus,  the  intermedius 
and  the  third  division  of  the  trigeminus.  Neurone  I  leads  from  the  periphery 
(the  tongue)  to  the  end-nucleus  ("nucleus  of  the  tractus  solitarius);  neurone  II  from 
the  end-nucleus  to  the  thalamus  ;  neurone  III  from  the  thalamus  to  the  cortical  gus- 
tatory  centre. 

Concerning  the  paths,  which  serve  to  conduct  the  gustatory  impulses,  the  following 
may  be  noted.       It  is  generally  accepted,   that  the  taste  impulses   from    the  anterior  two- 


Posi.  cphiinn  tracts 


Fig.  174. — Diagram  explaininR  Brown-St-quard's  hemilateral  lesion. 

thirds  of  the  tongue  are  conveyed  centrally  by  the  lingual  branch  of  the  trigeminus;  from 
the  posterior  third  of  the  tongue,  by  the  glossopharyngeus.  While  the  course  of  the 
taste-fibres  by  means  of  the  glossopharyngeal  nerve  is  readily  understood,  opinions  con- 
cerning the  path  followed  by  the  taste-fibres  from  the  anterior  two-thirds  of  the  tongue 
vary.  Thus,  it  is  assumed  by  some,  that  these  fibres  run  backward  in  the  chorda  tym- 
pani  to  the  ganglion  geniculi  and  thence  proceed,  either  through  the  great  superficial 
petrosal  nerve  to  the  spheno-palatine  ganglion  and  on  centrally  by  the  maxillary  division 


igo 


THE    FIBRE-TRACTS. 


of  the  trigeminus,  or  through  the  small  superficial  petrosal  nerve  to  the  otic  ganglion  and 
centrally  by  the  mandibular  nerve.  According  to  others,  the  chorda  fibres  reach  the 
glossopharyngeus  by  way  of  the  small  superficial  petrosal  and  the  tympanic  nerve.  It  is 
assumed,  further,  that  not  only  the  chorda  fibres,  but  also  the  gustatory  fibres  of  the 
glossopharyngeus,  by  way  of  the  small  superficial  petrosal  nerve,  reach  the  trigeminus  and 
in  it  pass  centrally.  Finally,  according  to  the  view  which  seems,  perhaps,  the  most 
reasonable,  the  chorda  fibres  pass,  by  way  of  the  chorda  tympani,  to  the  geniculate  gan- 
glion and  thence,  by  way  of  the  nervus  intermedins,  to  the  medulla  oblongata,  where  they 
form  a  descending  root,  which  ends   in  the   nucleus    tractus    solitarii,   that  is,   the  sensory 


Fig.  175. — Possible  conduction  paths  for  gustatory  impulsi 


end-nucleus  of  the  glossopharyngeus.  This  view,  further,  is  supported  by  the  experi- 
mental investigations,  which  have  shown,  that  removal  of  the  Gasserian  ganglion  or  intra- 
cranial section  of  the  ma.xillary  and  the  mandibular  divisions  of  the  trigeminus  are  not 
followed  by  loss  of  taste  in  the  anterior  two-thirds  of   the  tongue. 

f.  The  path  for  olfactory  impulses  leads  from  the  olfactory  mucous  membrane  by 
way  of  the  fila  olfactoria  to  the  bulbus  olfactorius,  thence  to  the  primary  centres  and 
from  the  latter  to  the  secondary  or  cortical  olfactory  centre  within  the  gyrus  hippocampi. 

g.  The  path  for  auditory  impulses  lies  within  the  nervus  cochleae.  Neurone  I 
conveys  the  stimulus  from  the  hair-cells  of  Corti's  organ  to  the  end-nucleus.  Neurone 
II  passes  from  the  end-nucleus  to  the  corpus  geniculatum  mediale  and  to  the  inferior 
colliculus,  the  fibres  forming  the  lateral  fillet.  Neurone  III  unites  the  corpus  geniculatum 
mediale  with  the  cortical  auditory  centre  within  the  gyrus  temporalis  superior. 


CENTRIFUGAL    PATHS. 


191 


h.  The  path  of  the  visual  impulses  Ues  within  the  nervus  opticus.  Neurone  I 
extends  from  the  retina  to  the  corpus  geniculatum  laterale,  to  the  pulvinar  and  to  the 
superior  colliculus.  Neurone  II  connects  the  corpus  geniculatum  laterale  and  the  pulvi- 
nar with  the  secondary  or  visual  centre  within  the  cortex  of  the  cuneus. 

II.    CENTRIFUGAL    TRACTS. 

I.  The  efferent  cortico-muscular  or  motor  tract  takes  its  origin  in  the  motor 
region  of  the  cerebral  cortex. 

Neurone  I:  through  the  internal  capsule  (knee  and  anterior  two-thirds  of  the  poste- 
rrorlimb),  the  basis  or  crusta  of  the  cerebral  peduncle  (middle  tiiree-fifths),  the  pons  and  the 
medulla  oblongata. 


pyramidal  tract 


Ant.  cereiro-afiinal  tract 
-   Lateral  curebro-spinal  tract 


Anterior  root 


a.  as  the  tract  of  the  motor  cerebral  nerves,  to  the  contralateral  nuclei  of  the  motor 
cerebral  nerves. 

b.  as  the  pyramidal  tract  proper,  to  the  spinal  cord — crossed  as  the  lateral  pyram- 
idal tract,  uncrossed  fin  the  medulla  oblongata)  as  the  anterior  pyramidal  tract — to  end 
around  the  ventral  horn-cells. 

NeuroTie  II:  origin  within  the  nuclei  of  the  motor  cerebral  nerves,  peripheral  course 
as  the  motor  cranial  nerves  to  the  muscles ;  or,  in  like  manner,  as 

Neurone  II:  origin  in  the  cells  of  anterior  horn  of  the  spinal  cord,  peripheral 
course    through  the  ventral  roots,   as  the  motor  spinal  nerves  to  the  muscles. 


192 


THE    FIBRE-TRACTS. 


2.  A  special  motor  speech-tract  does  not  exist.  The  speech-tract  is  identical 
with  those  paths,  which,  as  part  of  the  cortico-bulbar  tract,  pass  from  the  cortical  centre 
for  the  facial  and  hypoglossal  nerves  to  the  nuclei  of  the  nerves  necessary  for  speech. 

3.  A  cortico-rubral  motor  path  goes  to  the  spinal  cord  by  way  of  the  nucleus 
ruber,   as  follows  : 

Netirone  I:    from  the  cerebral  cortex  to  the  nucleus  ruber  ; 
Netirone  II:    nucleus  ruber,   tractus  rubro-spinalis,   spinal  cord  ; 
Neurone  III:    spinal  cord,   anterior  root,   muscle. 

4.  An  indirect  motor  path  passes  to  the  spinal  cord  by  way  of  the  pons  and  the 
cerebellum,  as  follows  :  frontal  and  occipito-temporal  pontile  tract — pontile  nucleus — cere- 
bellar cortex — nucleus  dentatus  cerebelli — superior  cerebellar  peduncle — nucleus  ruber— 
tractus  rubro-spinalis — spinal  cord — muscle  (Fig.    147). 

5.  In  addition  to  the  above  direct  and  indirect  motor  paths,  others  arise  within  the 
lower  brain-centres  and  pass  spinalward  ;  such  are  the  tractus  rubro-spinalis,  the  tractus 
tecto-spinalis  and  the  tractus  vestibulo-spinalis. 


B.    REFLEX    TRACTS. 

The  simplest  reflex  path  is  established  by  the  reflex  collaterals.  In  this  case 
only  two  neurones  share  the  entire  path,  the  transference  from  the  centripetal  to  the 
centrifugal    neurone    being    accomplished    by    means  of  the  collaterals  given    off  directly 

from  the  centripetal  or  afferent  neurone. 
The  release  of  the  reflex  may  be  in- 
duced, however,  by  intercalated  neurones. 
Thus,  between  the  centripetal  and  the  cen- 
trifugal neurone  a  third  neurone  may  inter- 
\'ene,  thereby  making  possible  the  transfer- 
ence of  the  impulse  conveyed  by  a  single 
centripetal  neurone  to  several  centrifugal 
ones.  Such  intercalated  neurones,  for  ex- 
ample, are  the  association-cells  of  the  spinal 
cord,  which  distribute,  by  means  of  their 
axones  and  collaterals,  impulses  to  many 
cells  within  the  cord-segments  of  higher  and 
lower  le\'els.  To  this  category  belongs,  fur- 
ther, the  posterior  longitudinal  bundle.  Im- 
pulses carried  to  Deiters'  nucleus  by  the 
\-estibuIar  nerve  may  be  distributed  to  the 
nuclei  of  the  eye-muscles  and  to  the  motor 
cells  of  the  cord  by  means  of  fibres,  which 
proceed  from  Deiters'  nucleus  and  run 
uithin  the  posterior  longitudinal  bundle. 
In  consequence  of  the  introduction  of  sev- 
eral neurones  between  the  centripetal  and 
r,  „  „         ,    .     ,  the  centrifugal  conduction,   the  entire  refle.x 

Fig.  177. — Reflex  paths  m  the  spmal  cord.    Broken  lines  rep-  . 

resent  neurones  distributing  impulses  to  other  levels.  mechanism    may    become    Very   complex.    ■ 


REFLEX  PATHS. 


193 


The  cerebellum,  with  its  afferent  and  efferent  paths,  calls  for  special  consideration. 
The  cerebellum  is  the  centre  for  the  refle.x  and  unconscious  maintenance  of  equilibrium, 
during  rest  as  well  as  during  changes  in  the  position  of  the  centre  of  gravity.  The 
centripetal  paths  lie  especially  within  the  nervus  vestibuli  and  within  the  ascending  fibre- 
systems  from  the  spinal  cord  and  from  the  medulla  oblongata.  These  ascending  paths 
from  the  cord  are  the  tractus    spino-cerebellaris   dorsalis  and  ventralis  ;    from  the  medulla 


Tract,  vfstibiiti^-sphiali 
FoiUrior  column  tract. 


FiC.   178. — Spino-cercbcllar  and  cerebcllofuKal  tracts.     Veslibulo-cercbcllar  tract-system  of  Deiters'  nucleus. 

oblongata  the  fibres  arising  within  the  nucleus  gracilis  and  cuneatus.  An  indirect  con- 
duction from  the  spinal  cord  is  perhaps  effected  by  the  tractus  spino-olivaris  or  Helweg's 
triangular  tract,  which  ends  within  the  inferior  olivary  nucleus,  and  thence  by  the  tractus 
olivo-cerebellaris  to  the  cerebellum,  by  way  of  the  restiform  body.  The  direct  and  the 
indirect  sensory  cerebellar  tract,  as  well  as  the  tracts  from  the  quadrigeminal  region,  are 
also  included  among  the  centripetal  paths.  By  means  of  the  cerebellofugal  tracts,  impulses 
may  be  carried  from  the  cerebellum  to  other  paths  and  by  means  of  the  latter,  in  turn, 
be  transferred  to  motor  paths.  The  chief  cerebellofugal  tracts  proceed  from  Deiters' 
nucleus  and  from  the  nucleus  dentatus.     From  Deiters'   nucleus  arise  the  tractus  vestibulo- 


194 


THE   FIBRE-TRACTS. 


spinalis  and  the  posterior  longitudinal  bundle,   the  last-named  system  coming  into  relation 
with  the  spinal  cord   and  with  the   nuclei   of    the   nerves  supplying  the  ocular  muscles — 


Tracti  o/  post.  coin. 


Tract,  vesiii'ilo  spinalh 


Tract,  rubr o-spinnUs' 


Tract,  spino-cerebellarts 


Fig.  179. — Cerebellopetal  and  cerebellofugal  tracts. 


that  is,  binding  together  the  centres  concerned  in  maintaining  equilibrium  and  relations 
to  space.  From  the  nucleus  dentatus  arises  the  superior  cerebellar  peduncle,  whose  fibres 
end  within  the  nucleus  ruber,  whence  the  tractus  rubro-spinalis  passes  to  the  spinal  cord. 


REFLEX    PATHS. 


195 


It  is  to  be  noted,  that  the  relations  of  the  cerebellar  hemispheres  with  the  spinal  cord 
are  homolateral  or  of  the  same  side.  Additional  cerebellofugal  paths  are  those  which,  as 
the  tractus  tegmentalis  pontis  et  bulbi,  run  within  the  tegmental  region  of  the  pons  and 
medulla  oblongata,  whereby  transference  to  motor  nuclei  may  in  turn  be  effected. 

If   the  maintenance  of   equilibrium  be  adjusted  to  a  voluntary  movement,   the   cere- 
bellum is  also  direcdy  stimulated  from  the  cerebral  corte-x.      The  paths  for  such  impulses 


Trncts  coming  frotn  higher  respit  atory 
centres  to  nucleus   respirator  ius 


Central  (nitclea-cortical) 
tract  of  vagus 


Sensory  ena-nucleus 
of  vagus 


sanguis 


Nn.thoracales 

Fig.  180. — Schematic  representation  of  the  tracts  chiefly  concerned  in  respiration. 


are  the  frontal  and  the  temporo-occipital  cortico-pontile  tracts,  which  end  in  the  pontile 
nuclei,  whence  the  conduction  to  the  cerebellum  is  by  the  middle  cerebellar  peduncle. 
In  addition,  the  pontile  nuclei  are  under  the  influence  of  the  pyramidal  tract,  from  which, 
within  the  pons,  collaterals  are  given  off  to  the  nuclei.  By  means  of  the  superior  cerebellar 
peduncle  (cerebellum-nucleus  ruber — thalamus — cortex),  the  cerebellum  sends  impulses  to 
the  cerebral  cortex  and  thereby  influences  conscious  innervation  (Figs.    145  and  147). 

Besides    the    cerebellum,    other    organs    that    preside    over    reflex    activity    call    for 
mention.      .Such  organs,  in  the  first  place,  are  the  thalamus  and  the  corpora  quadrigemina. 


196  THE    FIBRE-TRACTS. 

The  centripetal  paths  of  the  thalamus  are :  the  ascending  tract  of  the  medial  fillet,  the 
fibres  of  the  optic  tract  ending  within  the  pulvinar,  the  fibres  from  the  olfactory  centres 
and  the  fibres  from  the  cerebellum  by  way  of  the  superior  peduncle.  The  thalamofugal 
paths  lie  within  the  tractus  thalamo-spinalis,  the  tractus  rubro-spinalis  and  the  central 
tegmental  tract.  By  means  of  the  connections  between  the  thalamus  and  the  cerebral 
cortex,  impulses  coming  from  the  periphery  are  carried  to  the  cortex  and,  in  reversed 
direction,  activities  occurring  within  the  cerebrum  are   transferred  to  lower  lying  centres. 

The  centripetal  path  of  the  superior  colliculus  lies  within  the  tractus  opticus  and 
partly  within  the  lateral  fillet  ;  that  of  the  inferior  colliculus  within  the  lateral  fillet.  A 
centripetal  path  of  the  corpora  quadrigemina  is  afforded  also  by  the  ascending  tractus 
spino-tectalis,  associated  with  the  tractus  spino-thalamicus.  Fibres  pass  from  the  quadri- 
geminal  region  to  the  cerebellum  and  an  important  descending  path  forms  the  tractus 
tecto-spinalis,  the  path  from  the  quadrigeminal  bodies  to  the  spinal  cord.  Since  fibres 
from  the  optic  and  acoustic  nerves  end  within  the  quadrigeminal  region  and  the  path 
effects  the  transference  of  impulses  of  these  nerves  to  the  spinal  cord,  the  tecto-spinal 
tract  is  also  known  as  the  visuo-auditory  reflex  path. 

The  foregoing  by  no  means  completes  the  enumeration  of  the  reflex  paths,  since 
throughout  the  brain-stem  course  numerous  additional  tracts,  which  serve  to  unite  func- 
tionally related  centres.  In  this  connection,  it  is  only  necessary  to  recall  the  complex 
mechanism  of  the  medulla  oblongata,  in  which  different  nuclei  are  brought  into  the  most 
varied  relations,  whereby  numerous  simple,  as  well  as  the  most  complex,  reflex  proc- 
esses are  effected.  While  it  is  impracticable  here  to  consider  all  such  reflex  paths,  in 
order  to  obtain  some  notion  of  such  complicated  mechanisms,  we  may  represent,  by 
means  of  a  simple  diagram,   the  centres  and  tracts  chiefly  concerned  in  respiration. 

Respiration  is  maintained  by  the  stimulus  carried  to  the  respiratory  centre  through 
the  circulation.  In  addition,  the  reflexes  transmitted  by  the  vagus  also  come  into  con- 
sideration. In  Fig.  1 80,  the  respiratory  centre  is  represented  by  the  nucleus  respiratorius 
within  the  formatio  reticularis.  This  nucleus  stands  in  close  relation  with  the  sensory 
end-nucleus  of  the  vagus,  since  impulses  are  conveyed  to  it  by  the  collaterals  given  of? 
from  the  central  vagus-tract.  Moreover,  as  indicated  in  the  figure,  the  nucleus  respira- 
torius is  also  under  the  influence  of  the  higher  lying  respiratory  centres.  By  means  of 
the  paths  passing  from  the  respiratory  nucleus,  as  well  as  by  the  farther  connecting 
neurones,  the  irrpulse  is  transferred  to  the  motor  nuclei  of  certain  cerebral  nerves  and 
the  gray  substance  of  the  spinal  cord  and,  thence,  is  carried  by  the  motor  fibres  to  the 
muscles  concerned  in  respiration.  Thus,  the  impulse  is  carried  by  the  phrenic  nerve  to 
the  diaphragm;  by  the  thoracic  nerves  to  the  intercostales  and  levatores  costarum;  by  the 
cervical  plexus  to  the  scalene,  sterno-hyoid  and  sterno-thyroid  muscles  (depression  of  the 
larynx);  by  the  brachial  plexus  to  the  rhomboidei  and  pectoralis  minor;  by  the  accessorius 
to  the  sterno-cleido-mastoid  and  trapezius;  by  the  vagus  to  the  crico-arytaenoideus  posticus 
and  thyero-arytaenoideus  (widening  of  the  vocal  cleft)  and  the  levatores  veil  palatini  et 
uvulae  (elevation  of  the  soft  palate  and  the  uvula);  the  facial  nerve  to  the  facial  muscles 
(widening  of  the  nasal  apertures  and  the  oral  cavity).  The  paths  passing  from  the  nucleus 
respiratorius  course  in  the  medulla  oblongata  within  the  formatio  reticularis,  and,  as  shown 
in  the  accompanying  diagram,  numerous  motor  nuclei  are  brought  into  common  activity 
by  means  of  these  association  tracts  (Fig.    220). 


ASSOCIATION    PATHS.  197 


C.    ASSOCIATION    TRACTS. 

When  discussing  cerebral  localization,  it  was  pointed  out,  that  the  various  divisions 
of  the  brain  were  divided  in  a  general  way,  according  to  their  function,  into  higher  and 
lower  parts.  Functionally  the  highest  division  is  the  cerebrum,  with  the  cerebral  corte.x; 
the  lower  divisions  intervene  between  the  spinal  cord  and  the  cerebrum  and  include  the 
medulla  oblongata,  the  pons  and  the  cerebellum,  the  mid-brain  and  the  diencephalon  or 
inter-brain. 

All  nerve  tracts,  which  convey  to  the  central  nervous  system  the  most  varied 
impulses  from  the  individual  sense-organs  and  the  various  organs  within  the  body,  find 
their  immediate  ending  within  the  lower  brain-centres;  within  these  lower  centres  arise 
efferent  paths,  by  means  of  which  the  stimuli  received  are  again  projected  towards  the 
periphery  and  transferred  to  the  organs  of  movement.  In  this  manner  are  brought  about 
all  those  movements  that  we  designate  as  simple  and  complex  reflexes,  which  occur 
without  participation  of  our  consciousness.  The  impulses  conveyed  to  the  central  nerxous 
system,  however,  are  not  confined  to  the  subcortical  centres,  but  are  carried  by  other 
paths  to  the  cerebral  cortex,  where,  in  the  appropriate  sensory  centres,  impulses  are 
called  forth  which  psychically  correspond  to  what  w-e  designate  as  sensation.  This  impulse 
within  the  sensory  cortical  centres  continues,  so  long  as  the  stimulus  continues.  With 
the  stimulus,  the  impulse  disappears  and  therewith  the  sensation  also  ceases.  We  are 
able,  however,  to  picture  an  object,  even  when  we  no  longer  perceive  it,  or  to  recognize 
it  when  it  again  appears.  Therefore,  on  its  first  appearance,  the  stimulus  must  have 
called  forth  a  permanent  impulse,  in  addition  to  the  vanishing  sensory  impulse;  the  latter 
is  designated  the  concept  impulse.  The  retention  of  this  impulse  makes  possible  the 
recognition,  the  proving,  or  the  representation  of  the  object;  that  is,  there  remain  per- 
sistent traces  of  previous  sensory  or  motor  impulses,  the  so-called  latent  dispositions. 
These  latent  dispositions  or  subconscious  impressions,  when  later  awakened  by  new  impulses, 
render  possible  the  conscious  memory  or  conception  of  sensation  and  movement.  The 
ability  to  call  into  activity  and  to  convert  the  latent  dispositions  or  impressions  into 
conceptions  is  what  we  call  thought. 

In  addition  to  this  mnemonic  function,  the  cerebrum  possesses  the  associative  function. 
One  conception  can  awaken  others  by  reason  of  the  linking  together  of  the  latent  dis- 
positions. By  union  of  partial  conceptions  (visual,  gustatory,  olfactory,  tactile  and  other 
sensations),  the  complete  conception  is  attained;  by  the  blending  of  the  complete  con- 
ceptions, the  general  conceptions  are  formed.  In  this  way  are  "reproduced"  entire 
complexes  of  conceptions,  which  are  definitely  connected  and,  as  it  were,  lie  prepared; 
it  may  be,  however,  that  certain  complexes  of  conception  are  arranged  in  other  and  new 
sequences,  new  conceptions  being  thereby  "produced."  The  associative  function  consists, 
therefore,  in  the  reproduction  and  production  of  conceptions,  and  on  this  possibility  of  a 
definite  sequence  of  conceptions  depends  the  exercise  of  the  higher  psychic  processes, 
that  is,   thought. 

By  means  of  these  associative  processes,  the  individual  cortical  areas  within  the 
same  projection  and  memory  fields,  as  well  as  the  different  projection  and  memory  fields, 
are  brought  into  connection  with  one  another.     .Such  connection  between  the  dispositions 


198 


-Schematic  representation  of    the  physiologically  different  conductions.     Red.  centrifugal   tracts;   blue,  centrip. 
etal  tracts;  black,  intercentral  tracts. 


ASSOCIATIOX    PATHS.  199 

or  residues  of  the  same  kind  exists  everywhere  within  the  corresponding  cortical  areas. 
The  association  between  residues  of  different  kinds,  as  well  as  the  connection  of  projection 
are>is  with  memory  centres  and  of  the  \arious  projection  and  memory  centres  with  one 
another,  is  established  by  means  of  the  association  fibres,  which  as  short  and  long  fibres 
unite  adjoining  convolutions  and  remote  regions  respectively. 

Since,  however,  the  widely  different  processes  of  the  outer  world  and  of  the  body 
proper  gi\e  rise  to  the  formation  of  manifold  impressions  and  to  the  exercise  of  the 
most  simple  as  well  as  the  highest  psychic  processes,  something  further  always  occurs. 
The  influences  taken  up  by  the  organism  react  outwardly,  since  they  always  find  expres- 
sion in  the  various  movements  of  the  organs.  While  the  purely  reflex  reactions  are 
carried  out  unconsciously,  through  the  agency  of  the  lower  brain-centres  and  without 
the  participation  of  the  cerebrum,  the  voluntary  movements,  our  conduct  and  voluntary 
acts  are  dependent  upon  the  activity  of  the  cerebral  cortex,  every  action,  indeed,  being 
determined  by  conceptions  and,  in  the  final  analysis,  by  kinaesthetic  or  motor  concepts. 
These  relations  will  be  best  understood,  if,  in  conclusion,  we  consider  more  closely  those 
most  important  movements  concerned  in  speech,  by  means  of  which  our  entire  sensations, 
conceptions  and  thoughts  find  expression. 

When  discussing  cerebral  localization,  it  was  pointed  out,  that  in  right-handed, 
therefore,  in  the  majority  of  individuals,  the  speech-zone,  with  its  different  centres,  was 
located  within  the  left  hemisphere.  The  chief  centres  include  (Fig.  182):  the  se?isory 
speech-centre  (A),  within  the  posterior  third  of  the  superior  temporal  convolution,  where 
the  memory-pictures  of  the  heard  words  are  deposited — the  centre,  therefore,  for  the 
memory  of  word-tones — and  the  >no/or  speech-centre  {M),  within  the  posterior  third  of 
the  inferior  frontal  convolution,  in  whose  cells  the  memory-pictures  of  the  spoken  words 
lie  and  on  whose  integrity  depends  the  ability  to  carry  out  the  coordinated  movements 
of  certain  muscles  necessary  for  speech. 

These  two  speech-centres,  the  sensory  and  the  motor,  stand  in  close  relation  with 
each  other,  the  latter  dependent  upon  the  former,  since  speech  is  acquired  by  repetition 
of  the  word-sounds  heard.  On  observing  the  development  of  speech  in  the  child,  we  find 
in  the  connection  of  these  two  centres  the  basis  for  the  possibility  of  pronouncing  by 
repeating  but  without  understanding.  The  development  of  speech  teaches,  moreover,  that 
speech  proper,  that  is,  the  intelligent  utterance  of  sounds,  in  contrast  to  their  mere  repeat- 
ing, is  preceded  by  an  understanding  of  speech  without  speaking — a  stage  of  ' '  normal 
deaf-mutism."  The  child  understands  much,  but  speaks  little  or  nothing  of  what  it 
understands  ;  it  is,  for  the  time,  deaf-mute.  Therefore,  an  intimate  connection  is  early 
established  between  the  memory  of  the  word -sound  or  the  acoustic  word  (^A)  and  the 
idea  {B).  In  Fig.  182,  this  close  connection,  as  well  as  that  between  the  sensory  and 
motor  speech-centres,  is  represented  by  the  double  line,  A  —  D.  In  this  relation  it 
should  be  emphasized,  that  the  idea-centre  {B)  is  represented  as  a  definitely  bounded 
cortical  area  only  as  a  schematic  expedient,  and  that,  as  a  matter  of  fact,  we  must  con- 
ceive the  formation  of  the  idea  as  a  complex  process  involving,  more  or  less,  the  entire 
cerebral  cortex. 

From  this  speech-comprehension  without  speaking  {a}  —  a-  —  a  —  A  —  B)  and  the 
first  mere  repeating  of  spoken  words  {a^  —  a^  —  a  —  A—  M  —m  —  ni^  —  m^),  later  comes 
the  repeating  of   words  with  the   understanding  of   speech;    that  is,  speech  proper.     The 


THE    FIBRE-TRACTS. 


/2.o/iti<ms 


Fig,  182. — Scheme  of  spoken  and  written  speech.  B,  conception  centre;  M,  motor  speech-centre  (,Broca)\  A,  sensory 
speech-centre  {.Wernicke);  0,  visual  letter-centre;  m,  motor  centre  (facial,  lingual  and  laryngeal  musculature);  a,  auditory 
centre;  o,  visual  centre;  H,  motor  centre  for  hand;  m'  in-  h'^  h-  —  cortico-muscular  tracts  for  speaking  and  writing; 
fli  a-  0^  o2  —  auditory  and  visual  tracts. 


ASSOCIATION  PATHS. 


latter  first  takes  the  path  :  B  —  A  —  M—  m  —  w'  —  m- ;  later,  in  consequence  of  the 
connection  B  —  M,  it  follows  :  B  —  M—  m  —  ?«'  —  7n^.  The  centre,  wz,  represents  the 
motor  centre  proper,  in  the  lower  third  of  the  precentral  convolution  (the  motor  centre 
for  the  face,  tongue,  and  larynx).  The  path,  »«',  is  the  motor  cortico-bulbar  tract,  which 
passes  through  the  knee  of  the  internal  capsule,  the  crusta  or  base  of  the  cerebral 
peduncle  to  the  nuclei  of  the  appropriate  motor  cerebral  nerves.      Path  mf  is  the  periph- 


ll'rWng-csKtre 


Fig.    183. ^Connections   of  the 


Sightc 


ndividual   centres   of  the   speech    zone, 
through   the   brain. 


eral  motor  neurone  from  the  motor  nucleus  to  the  muscle.  Likewise,  close  to  the 
sensory  speech-centre  (/4),  the  auditory  centre  proper  is  represented  (a).  The  path  a' 
shows  the  course  of  the  auditory  tract  as  far  as  the  medial  geniculate  body  ;  the  patTi  t^ 
is  the  la.st  neurone  in  the  auditory  tract,  which  extends,  by  way  of  the  internal  capsule, 
from  the  geniculate  body  to  the  cortical  auditory  centre. 

The  foregoing  connections  represent  speech  in  the  more  limited  sense;  later,  as  the 
result  of  learning  written  speech — reading  and  writing — the  expansion  to  speech  in  its 
widest  sense  follows.  By  written  speech  is  understood  the  speech  of  the  letters  ;  the  latter 
are  to  be  regarded  not  as  signs  for  ideas,  as  hieroglyphics,  but  as  signs  for  sounds.     We 


202  THE    FIBRE-TRACTS. 

learn  to  separate  the  individual  words  into  syllables  and  letters,  each  simple  sound,  vocals 
and  consonants,  being  associated  with  a  visual  letter-picture  ;  by  copying  the  optical 
picture  of  the  letter  we  learn  to  write.  The  sensory  speech-centre  or  the  acoustic  word 
now  comes,  therefore,  into  closer  relation  with  the  visual  apparatus.  Not  only  the 
acoustic  word,  but  also  the  motor  word,  or  the  centre  for  the  motor  memory-pictures  of 
the  words,  becomes  connected  with  the  visual  letter-centre,  or  visual  centre,  O,  within 
the  gyrus  angularis ;  here  the  memory-pictures  of  the  written  characters  are  deposited, 
since  for  reading  the  sensory  and  motor  speech-centres  are  necessary.  For  writing,  more- 
over, connection  is  established  between  the  visual  centre,  O,  and  the  motor  centre  for 
the  upper  extremity  within  the  middle  part  of  the  precentral  convolution,  the  centre,  N, 
for  the  musculature  of  the  hand,  wherein  the  grapho-motor  memories  are  developed 
through  practice.  In  Fig.  182,  this  locality  is  represented  by  two  superimposed  ovals, 
since  the  existence  of  a  distinct  writing-centre  is  not  accepted. 

Reading  is  accomplished,  therefore,  by  the  path  :  o^  —  o-  —  o  —  O  —  A  or  M  —  B ; 
spontaneous  writing  by  :  B  —  A  or  M—  O  —  H  —  /;'  —  K-.  The  path  o^  represents  the 
first  neurone  of  the  visual  path  leading  to  the  lateral  geniculate  body;  the  path  0^  is  the 
second  neurone  from  the  geniculate  body,  by  way  of  the  internal  capsule,  to  the  visual 
centre  proper,  o.  The  latter  is  shown  in  the  diagram  in  the  occipital  pole,  but,  as  well 
known,  the  centre  is  localized  chiefly  within  the  cortex  of  the  cuneus,  particularly  sur- 
rounding the  calcarine  fissure.  The  path,  h^,  represents  the  course  of  the  motor  tract 
from  the  arm  centre  through  the  internal  capsule  and  the  brain-stem  to  the  spinal  cord; 
the  path,  h^,  is  the  peripheral  motor  neurone  to  the  muscles  of  the  hand. 

In  Fig.  183,  the  connections  of  the  individual  speech-centres  are  represented  schem- 
atically in  horizontal  section.  The  course  of  the  tracts  from  one  hemisphere  to  the  other, 
through  the  corpus  callosum,   is  to  be  noted. 

On  Fig.    182,   we  may  trace  the  following  paths  : 

Speech  comprehension  :  a'^  —  a~  —  a  —  A  —  B ; 

Repeating  words  :  a)-  —  a^  —  a  —  A  —  M  —  m  —  vO-  —  ni- ; 

Spontaneous  speech  :  B  —  A  —  M—  m  —  m'-  —  m^ 
B  —  M  —  in  —  ni^  —  nt'- 

Reading  :  d^  —  o^  —  o  —  O  -  A  or  M—  B; 

Reading  aloud  :  o^  — 0^  —  0—  O— A  ox  M—  B—  Rf—m  —  m'^  —  in?-; 

Spontaneous  writing :  B  —  A  ox  M  —  O  —  H ~  h^  —  h?-; 

Copying  :  d^  —  o'-  —  0  —  O  —  H—  /i^  —  h- ; 

Dictated  writing  :  a^  —  a-  —  a  —  A  or  M—  O  —  H  —  h^  —  Ifi. 

At  the  same  time,  the  diagram  explains  the  different  types  of  the  disturbances  of 
speech  or  aphasia. 

A  lesion  of  the  speech-centre,  M,  leads  to  cortical  motor  aphasia.  The  patient  can 
neither  speak  spontaneously,  nor  repeat;  moreover,  since  reading  and  writing  depend 
upon  the  integrity  of  the  sensory  as  well  as  of  the  motor  speech-centre,  reading,  spon- 
taneous writing  and  dictated  writing  are  also  impaired.  On  the  other  hand,  the  patient 
understands  what  is  spoken,   since  A  is  intact,   and  can  copy  writing. 


ASSOCIATION    PATHS.  203 

A  lesion  of  the  sensory  speech-centre,  A,  leads  to  cortical  sensory  aphasia.  In  the 
first  place,  comprehension  of  speech  is  lost;  further,  repetition,  reading  and  dictation 
writing  are  suspended,  while  spontaneous  writing  and  copying,  as  well  as  speech,  are 
retained.  In  speaking,  however,  the  patient  manifests  the  symptoms  of  paraphasia,  that 
is,  the  interpolation  of  incorrect  words  and  exchange  and  mutilation  of  words. 

Destruction  of  both  chief  centres,  the  motor  and  the  sensory,  leads  to  total  aphasia. 

When  the  efferent  path  from  the  motor  speech-centre,  M,  is  interrupted  by  a  sub- 
cortical effusion,  the  clinical  picture  of  subcortical  motor  aphasia  or  word-dumbness 
appears;  when  the  lesion  invokes  the  path  to  the  sensory  speech-centre,  subcortical  sen- 
sory aphasia  follows.  These  subcortical  aphasias  leave  inward  speech  intact,  and  the 
ability  to  read  and  write  are  retained.  On  the  other  hand,  in  subcortical  motor  aphasia, 
voluntary  speech,  repeating  and  reading  aloud,  are  suspended  or  involved;  in  subcortical 
sensory  aphasia,  speech-comprehension,  repeating  and  dictation  writing  are  wanting  or 
impaired. 

If  the  path  from  the  idea-centre  to  the  motor  speech-centre  (BM )  be  interrupted, 
the  patient  is  said  to  be  affected  with  transcortical  motor  aphasia,  with  loss  of  voluntary 
speech  and  writing;  if  the  path  from  the  sensory  centre  to  the  idea-centre  be  broken, 
the  resulting  condition  is  termed  transcortical  sensory  aphasia,  with  loss  of  the  compre- 
hension of  speech  and  of  writing. 

An  interruption  of  the  path  uniting  the  sensory  and  motor  speech-centres  (AM) 
leads  to  the  so-called  conduction  aphasia.  The  ability  of  repeating  words  is  impaired  ; 
speech  and  comprehension  of  writing  and  the  ability  to  copy  are  retained,  as  well  as 
spontaneous  speech  and  writing;  the  performance  of  these  functions,  however,  is  attended 
with  the  manifestations  of  parapliasia  and  paragraphia. 


PART  III. 

SERIAL  SECTIONS  THROUGH  THE  BRAIN-STEM 
OF  A  FOUR-YEAR-OLD  CHILD 


FROM  THE  ANTERIOR  END  OF  THE  CORPUS  CALLOSUM  TO  THE 
QUADRIGEMINAL  REGION 


FROM    CORPUS    CALLOSUM  TO  QUADRIGEMINAI.   REGION.  207 


2o8  SERIAL    SECTIONS    THROUGH    THE    BRAIN-STEM. 


FROM    CORPUS    CALLOSUM  TO  QUADRIGEMINAL  REGION.  209 


SERIAL    SECTIONS    THROUGH    THE    BRAIN-STEM. 


FROM    CORPUS   CALLOSUM  TO  QUADRIGEMIXAL  REGION.  211 


■B    E   B 

»  »  o 

s  S 


SERIAL    SECTIONS   THROUGH    THE    BRAIN-STEM. 


FROM    CORPUS    CALLOSUM  TO  QUADRIGEMINAL  REGION.  213 


^    *    rt 


214 


SERIAL    SECTIONS    THROUGH    THE    BRAIN-STEM. 


FROM    CORPUS    CALLOSUM  TO  OUADRIGEMINAL  REGION.  215 


2l6 


SERIAL    SECTIONS   THROUGH    THE    BRAIN-STEM. 


FROM    CORPUS    CALLOSUM  TO  QUADRIGEMINAL  REGION.  217 


•S  s 


H    S 


218 


SERIAL    SECTIONS    THROUGH    THE    BRAIN-STEM. 


FROM    CORPUS    CALLOSUM  TO  OUADRIGEMINAL  REGION.  219 


■5  :5  ?  E 
ja    tj    a;    5 

"S  "o  -s  .0 


SERIAL    SECTIONS    THROUGH    THE    BRAIN-STEM. 


FROM    CORPUS    CALLOSUM  TO  QUADRIGEMINAL  REGION.  221 


SERIAL    SECTIONS    THROUGH    THE    BRAIN-STEM. 


g  "1  c    n 

^  u  '^  '^ 

S  »  £•  S 

-2  ^  u 


E  -3 


i  H  .S 


S     V,     fe     g 

lis' 


I  fe  i  ° 

»    "     D     0. 

"  ^5  a 

2      01      V.      " 

&<  £  .2  a 


o.  S  • 


FROM    CORPUS    CALLOSUM  TO  QUADRIGEMINAL  REGION.  223 


224 


SERIAL    SECTIONS    THROUGH    THE    BRAIX-STEM. 


g  =  =  c 

"5     0     3"= 


§  ^  ^ 


FROM    CORPUS    CALLOSUM  TO  OUADRIGEMINAL  REGION. 


225 


e^-s  g 


226 


SERIAL    SECTIONS    THROUGH    THE    BRAIN-STEM. 


FROM    CORPL-S    CALLOSUM  TO  OUADRIGEMIXAL  REGION. 


27 


3  1 .2 


228  SERIAL    SECTIONS    THROUGH    THE    BRAIN-STEM. 


'■a'S  ^ 
Effl.S 


fl 


6  i:  « 


%^ 


FROM    CORPUS    CALLOSUM  TO  OUADRIGEMINAL  REGION.  229 


230 


SERIAL    SECTIONS    THROUGH    THE    BRAIN-STEM 


FROM    CORPUS   CALLOSUM  TO  QUADRIGEINIINAL  REGION.  231 


1(3  a  J3  u  a 


232 


SERIAL    SECTIONS    THROUGH    THE    BRAIN-STEM. 


o&   E^ 


FROM    CORPUS    CALLOSUM  TO  OUADRIGEMINAL  REGION.  233 


>     S     P. 


tjo  -^  y=: 


.S   c  S 

X    3  -B 


^34 


SERIAL    SECTIONS    THROUGH    THE    BRAIN-STEM. 


B 


FROM  THE   CAUDAL   END   OF  THE   MEDULLA  OBLONGATA 
TO   THE   QUADRIGEMINAL   REGION 


236 


SERIAL    SECTIONS    THROUGH    THE    BRAIN-STEM. 


^       ci 


FROM    MEDULLA    OBLONGATA  TO    OUADRIGEMLNAL   REGION.       237 

•g8g.s£.9fg-3g°;-g'"fg 

a  ■=  •§    a  -S    ;  •«   i  -  ■£    •-  .2.  ii  .S 
»    S    s    S  ■^   S   -^    ?    'i   V.    a   .t    5    " 


sill's*^  £°.p|| 

1  N  -s  2  £  °  i  s :  ^  I  g 


-   ■=    "•    c    S-    - 

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SELECTED    REFERENCES. 

The  following  list  includes  important  books  and  monographs  relating  to  the  anatomy  of 
the  Central  Nervous  System,  which  the  student  may  consult  with  advantage.  Extended  bib- 
liographies will  be  found  in  Obersteiner  and  in  the  year-books  of  Anatomy  and  Neurology. 

Barker,  L.  F.  The  Nervous  System  and  its  Constituent  Neurones.  1899. 
Bechterew,  W.  Die  Leitungsbahnen  im  Gehirn  und  Ruckenmark.  1^99. 
Brodmann,    K.      Die    Cortexgliederung    des    Menschen.      Jour.     f.    Psychol,    u.    Neurol., 

Bd.   X.,  1907. 
Brodmann,   K.      Die  feinere  Anatomie  des  Grosshirns.      Lewandowsky's    Handbuch  der 

Neurologic,  19 10. 
Cajal,   S.    Ramox  v.      El   systema    nervioso    del    Hombre  e    de   los  Vertebrados.      1902. 
Charpv,    a.       Systeme     Nerveux.        In    Poirier's     Traite    d' Anatomie     Humaine,    Tome 

III.,    1899. 
Cunningham,    D.   J.     Surface   Anatomy   of   the    Cerebral    Hemispheres.      1892. 
Dalton,  J.   C.      Topographical    Anatomy    of  the    Brain.      Atlas.      1885. 
Dejerine,  J.     Anatomie  des    Centres    Nerveux.      1901. 

DoGiEL,  A.   S.     Der  Bau  der  Spinalganglien  des  Menschen  und  der  Saugethiere.     1908. 
Donaldson  and  Davis.      Areas    of    Cross-Sections    of    the    Spinal    Cord    at    the    Level 

of    each    Spinal    Nerve      Journal    of   Comparative   Neurology,  Vol.   XIII.,    1903. 

Edinger,   L.     V'orlesungen   ueber   den    Bau   der  nervosen    Zentralorgane.      1908. 
Flechsig,   p.     Die    Leitungsbahnen    im    Gehirn   und    Ruckenmark.      1876. 
Gehuchten,   van  a.      Anatomie    du    Systeme    Nerveux    de  1' Homme.      1906. 
Haberlin,  C.     Zur  Topographic  der  Hirnventrikel.      Arch.  f.  Anat.   u.   Entwick.       1909. 
Held,   H.     Die    Enstehung   des    Nervengewebes.      1909. 
His,  W.     Die    Formentvvickelung   des    menschlichen    Vorderhirns.      1889. 
His,  W.     Die    Entvvickelung   des    menschlichen  Gehirns.      1904. 

Horsley,   V.     The    Cerebellum  :      Its    Relation    to    Spacial    Orientation   and    to    Loco- 
motion.    Boyle    Lecture.      1905. 

Jacobsohn,   L.      Ueber    die     Kerne     des     menschlichen    Hirnstamms.       Akademie     der 
Wissenschaften,    Berlin.      191 1. 

Jakob,   C.      Vom    Tierhirn    zuni    Menschenhirn.      Atlas.      1911. 
Johnston,  J.    15.     The    Nervous    System    of   Vertebrates.      1906. 

Johnston,   J.    \',.     The    Morphology   of   the    Fore-Brain    Vesicle   in  Vertebrates.     Journal 
of   Comparative     Neunjlogy    and    Psychology.      Vol.    XIX.,     1909. 

279 


28o  SELECTED    REFERENCES. 

Kaes,  T.      Die    Grosshirnrinde    des    Menschen    in    ihren    Massen    u.     in    ihrem    Faserge- 

halt.      1907. 
KoELLiKER,   A.      Handbuch    der    Gewebelehre.      Band  II.,  1S96. 
KUPFFER,    K.      Die    Morphologie    des    Central  nervensystems.      In    Hertwig's    Handbuch 

der    Entwickelungslehre.      Bd.    II.,    Th.    3  ,    1906. 
Lenhossek,   M.      Der  feinere  Bau  des  Nervensystems.      1895. 

Lewandowsky,   M.      Handbuch  der  Neurologic.      I.    Allgemeine  Neurologic.      1910. 
Malone,   E.      Ueber  die  Kerne  des  menschlichen  Diencephalon.      Akademie  der  Wissen- 

schaften,   Berlin.      19 10. 
Marburg,   O.      Mikroskopisch-topographischer   Adas   des   menschlichen   Zentralnervensys- 

tems.      19 10. 
MoNAKOW,  C.      Der  rothe  Kern,  die  Haube  u.  die  Regio  subthalamica  bei  einige  Siiuge- 

thieren   u.   bei    Menschen.       Arbeiten    a.    d.    Hirnanatomischen    Institut    in    Ziirich. 

Bd.   III.,    1909. 
Nebelthau,    E.      Schnitte  durch  das  menschliche  Gehirn.      189S. 
Neumayer,   L.      Histo-   und    Morphogenese    des    peripheren    Nervensystems,    der    Spinal- 

ganglien   und  des   Nervus    sympathicus.       In   Hertwig's   Handbuch    der   Entwickel- 
ungslehre.     Bd.   II.,  Th.    3,  1906. 
Obersteiner,  H.      Anleitung  beim  Studium  des  Baues  der  nervosen  Centralorgane.      1912. 
Parker,   G.   H.      The   Phylogenetic   Origin  of   the   Nervous  System.      Anatom.    Record, 

Vol.    IV.,    1910. 
Retzius,    G.      Das  Menschenhirn.      1896.      Atlas  of  special  regions. 
Sachs,   E.      On  the  Structure  and   Functional   Relations  of  the  Optic  Thalamus.      Brain, 

Vol.   CXXVI.,  1909. 
Sabin,   F.  R.      Atlas  of  the  Medulla  and  Midbrain.      1901. 

Schafer  and  Symington.     Neurology.      In  Ouain's  Anatomy,  Vol.  III.,  1908. 
Smith,    E.      A    new   Topographical    Survey  of    the    Human    Cerebral    Corte.x.      Jour,    of 

Anatomy  and  Physiology,  Vol.  XLI.,  1907. 

Streeter,  G.  L.  Die  Entwickelung  des  Nervensystems.  In  Keibel  and  Mall's  Hand- 
buch d.  Entwickelungsgeschichte  d.  Menschen.      Bd.  II.,  1911. 

Tilney,  F.  Contribution  to  the  Study  of  the  Hypophysis  Cerebri,  with  Especial  Refer- 
ence to  Its  Comparative  Histology.      1911. 

Vogt,  C.  La  myeloarchitecture  du  thalamus  du  cercopitheque.  Jour.  f.  Psychol,  u. 
Neurol.,  Bd.   XII.,  1909. 

Wernicke,   C.     Atlas  des   Gehirns.      1897. 

Ziehen,  T.  Die  Morphologie  des  Centralnervensystems  der  Siiugetiere.  In  Hertwig's 
Handbuch  der  Entwickelungslehre.      Bd.    I!.,  Th.    3,    1906. 

Ziehen,  T.  Die  Histogenese  von  Hirn-  und  Riickenmark.  In  Hertwig's  Handbuch  der 
Entwickelungslehre.      Bd.    II.,  Th.    3,    1906. 

Ziehen,   T.      Nervensystem.      In  Bardeleben's  Handbuch  der  Anatomie.      1S99. 


NDEX 


Abducens.  176 
Accessorius,  185 
Acervulus,  56 
Acusticus,  179 
Ala  cinerea.  82 

lobuli  centralis,  73 

uvulae.   75 
Alveus,  45,   120 
Angulus  gjri  olfact.  lat..  28 
Ansa  lenticularis.  144.  219 

peduncularis,  144.  219 
Anterior  column.  90 
tracts,  161 

commissure,  135 

ground  bundle,  161 
Apertura  medialis  ventric.  quarti  (Magendii),  80 

lateralis  ventric.  quarti   (Lnschkaej,  80 
Aphasia,  202 
Apraxia,  130 

Aquaeduct.  cerebri  Sylvii,  68 
Arachnoidea  cerebri,  88 

spinalis,  93 
Arachnoidal  villi  (Pacchioni),  88 
Arbor  medullaris,  76 

vermis  vitae,  76 
Arcuate  fibres,  167,   170 

nucleus,  84,  170 
Area  acustica,  82 

medial,  trigoni  N.  XII.,  82 

parol  factoria   (Broca),  27 

plumiforniis.  82 

postrema,  82 
Asccnsus  medullae  spinalis,  9 
Association  cells,  160 

area,  171 

centres   (Fleclisig),  127 

conduction,   133 

fibres,  1.34 

tracts,  197 
Astrocytes,  106 
Astropilemma,  106 
Auditory  centre,  126 

path,  190 
Axis-cylinder,  in 

process,  109 
Axone,  109 

Baillarger's  stripe,  y).  115 
Band  of  Giacomini,  34 


Bandelette  mediale  (Gotnbault-Philippe),  166 
Basal  ganglia,  46 
Basket  cells,  154 
Basis  cerebri,  12 

pedunculi,  67 
Bechterew's  nucleus.  181 
Bipolar  cells,  109 
Brachia  cerebelli,  76,  156 
ad  cerebrum.  76 
ad  Corp.  quadrig.,  76 
ad  medullam,  76 
ad  pontem,  76,  155 

conjunctiva,  70,  76,   156 

corp.  mamillar.,  57 

pontis,  76.  155  ' 

quadrigemina,  66 
Brain  development,  4 

form,  9 

membranes.  86 

morpholog>',  3 

size,  10 

weight,  10 
Brain-sand.  56 
Brain-stem,  6 
Brain-vesicles,  4 
Broca's   callosal    stalks,   30 

centre,  128 

convolution,  20 

diagonal  band,  30 

field.  27 
Bulbus  cornu  post..  43 

olfactorius,  27.  1 18 
Burdach's  column,  78,  164 

Cajal's  cells,  iir,  115 
Calamus  scriptorius,  81 
Calcar  avis,  43 
Callosal  convolutions,  36 

radiations.  40 
Calloso-marginal  fissure,  23 
Capsula  externa,  48,  135 

extrema,  50,  136 

interna,  48,  61,  142 
Cauda  equina.  9 
Cavum  epidurale,  93 

interdurale.  93 

psaltcrii.  J4 

septi  pellucidi,  41 

subdurale.  93 


282 


INDEX. 


Central  tegmental  tract,  151 
Centrifugal  tracts,  131,  191 
Centripetal  tracts,  131,  186 
Centrum  medianum   (Luys),  60,  228 

semiovale   (Vieussens),  39    ' 
Cerebellar  cortex,  154 

falx,  87 

peduncles,  inferior,  76,  170 
middle,  76,  157 
superior,  76,  156 

tent,  76 

tracts,  155 
Cerebellum,  72,  152 
Cerebral  cortex,  39 

crura,  66 

ganglia,  46 

mantle,  18 

nerves,  172 

nerves,  table,  14 

peduncles.  66 
Cerebro-spinal  fluid,  88 
Cerebrum,  11 
Chiasma  opticum,  ^7,  174 
Ciifgulum,  13s,  149 
Cisterna  ambiens,  88 

cerebello^medullaris,  88 

chiasmatis,  88 

corporis  callosi,  88 

fossae  Sylvii,  88 

interpeduncularis,  88 
Clarke's  column,  90,  159 
Claustrum,  50 
Clava,  78 

Climbing  fibres,  155 
Cochlearis,  179 
Colliculus  facialis.  82,  178 

subpinealis,  66 
Column-cells,  160 
Columna  fornicis,  44 
Columnae   griseae,   gi 
Comma  bundle  of  Schultze,  166 
Coramissura  anterior,  i6,  135 
alba,  9 1 
grisea,  91 

cerebri  magna,  40 

habenularum.  55 

hippocampi,  44,  135.  146 

posterior  cerebri,  56 
medullae,  go 

supramamillaris,  225 
Commissure-cells,  160 

fibres,  135 
Confluens  sinuum,  88 
Conus  medullaris,  9,  89 

terminalis,  89 
Convolutions,  see  Gyri 
Cornu  Arrmonis,  45,  120 


Cornua  ventriculi  lat.,  40,  41,  42 
Corona  radiata,  135 
Corpora  candicantia,  56,  147 

geniculata,  56 

mamillaria,  56,  147 

restiforraia,   77,   170 
Corpus  album  subrotund.,  $9 

callosum,  14,  40 

fornicis,  44 

geniculatum,  56 

Luys,  61 

mamillare.  56,   147 

meduUare  cerebelli,   75 

parabigeminum,  271 

patellare  (Tschish),  60 

pineale,  55 

resti  forme,  77,  170 

striatum,  41,  48,  144 

subthalamicum,  61,  224 

trapezoides,  i7g 
Cortical  cells,  3g 
Cortico-bulbar  tract,  138 
Cortico-spinal  tract,  138 
Crura  cerebelli,  76,  155 
ad  cerebrum,  76 
ad  Corp.  quadrig.,  76 
cerebelli  ad  meduUam,  77 
ad  ponteni,  76 

fornicis,  44 
Crus  fornicis,  44 
Culmen  cerebelli,  73 
Cuneus,  24 
Cuticle-plate,  3 

Declive  cerebelli,  73 

Decussation,  cerebellar  peduncles,  156 

fillet.  167 

Forel's,  274 

Meynert's,  274 

motor,  77,  138 

pyramidal,  77,  138 

sensory.  167 
Deiters'  cells,  iii 

nucleus,  181 
Dendrites,  in 
Development,  brain,  4 

ependyma  cells,  103 

nerve-cells.  105 

neuralgia.  104 

spinal  cord.  8 

spinal  ganglia,  105 
Diagonal  band  of  Broca,  30 
Diaphragma   sellae   turcicae,   88 
Diencephalon,  52.  150 

summary.  63 
Digitationes  hippocampi,  43 
Direct  cerebellar  tract,  161 
Direct  sensory  cerebellar  tract,  170 


INDEX. 


283 


Dura  mater  cerebri,  87 
spinalis,  93 

Edinger-Westphal  nucleus,  176 

Embolus,  83 

Eminentia  collaterale,  43 

medialis,  81 

pyraniidalis,  71 

saccularis,  38 
Encephalon,  3 
End-brain,  4,  17,  134 
Endogenous  fibres,  160 
End-plate,  21 
Ependyma  cells,    103 

nuclear  zone,   103 
Ependyniium,  103 
Epicerebral  space,  88 
Eyes,  movements  of,  184 

Facialis,  178 
Facial  knee,  178 
nucleus.    178 
Falx  cerebelli,  87 
cerebri,  87 
major.  87 
minor,  87 
Fascia  dentata   (Tarini),  32 
Fasciculus  ant.  propr.,  161 
arcuatus,  135 

(Foville),  71 
cerebro-spinalis  ant..  139 

lateralis,  139 
cuneatus,  77,  90,  164 
fronto-occipitalis,  135,  207 
gracilis,  77,  go,   164 
lateral,  propr.,  162 
lenticularis  (Forel),  222 
longitudinal,  dorsal.   (Scliiitz),  148,  I51 
inferior,  135 
medialis,   148,  153,  182 
superior,  135 
praedorsalis,  153 
mamillaris  princeps.  147 
mamillo-tegmcntalis,  147 
maniillo-thalamicus,  147 
obliquus  pontis,  71 
pyramidalis,  82,  138 
retroflexus  (.\Icynert),  148 
solitarius,  185 
sulco-marginalis,  161 
tegmento-mamillaris,  147 
thalamicus,  224 
thaIamo-mamillari«,    147 
uncinatus,  135 
Vicq  d'Azyr,  147 
Fasciola  cinerea,  a 
Fastigium,  79 
Fibra  pontis,  71 


Fibrae  arciformes,  70,  155 
arcuatae,  78,   167 

ext.  dorsales,  170,  247 
ext.  ventrales,  170,  247 
internae,  167,  242 
pontis  profundae,  82 
superficiales,  82 
propriae,  134 
terminales,  115 
Fibrillar  network,  112 
Fila  lateralia  pontis,  71 

olfactoria,  27,  118,  144 
Fillet,  lateral,  179 

mesial,  167 
Filum  terminale,  g,  89 
Fimbria,  t,^,,  44 
Fissura  calcarina,  24 
cerebri  lat.,  18 
longitud.,  II 
transversa,  12 
chorioidea,  42 
collateralis.  24 
hippocampi,  24 
longitudinalis  cerebri,  11 
mediana  ant.,  77,  89 
parieto-occipital.,  20,  24 
prima  (His),  26 
rhinica.  24 
Rolandi,  19 
transversa  cerebri,  12 
Flechsig's  association  centre,  127 

direct  cerebellar  tract,   161,   170 
Feltwork,  interradial,  115 
supraradial,  115       * 
Flocculus,  75 

accessory,  75 
peduncle  of,  75 
Folium  vermis,  74 
Foramen  caecum,  77 
diaphragmatis,  88 
interventriculare,  8,  43 
Luschkae,  80 
Magendii,  80 
Monroi.  8,  43 
Forceps,  40 

Fore-brain,  derivatives,  65 
Ford's  tegmental  decussation,  274 
Formatio  reticularis,  85 
Fornix,  44,  137,  146 

longus  (Forcl),  146 
periphcricus  (Arnold),  135.  149 
pillars  of,  44 
transversus,  44,   146 
Fossa  cerebri  lateralis   (.Sylvii),  18 
interpcduncularis   (Tarini)    68 
mediana,  81 
rbomboidea,  81 
Fountain  decussation,  273 


284 


INDEX. 


Frenulum  veli  medullaris.  70 
Frontal  pontile  tract,  137 

lobe,  ig 
Ftiniculus  anterior,  90,  161 

lateralis,  90,  161 

posterior,  90,  163 

separans,  82 
Fourth  ventricle,  79 

Ganglioblasts,  106 
Ganglion-strand,  105 
Ganglion  ectomamillare,  68 

habenulae,  61,  148 

interpedunculare  (Gudden),  69,  14S 

profund.  mesencephali,  69 

tegmenti  dorsale,  69,  147 
Gennari's  stripe,  39 
Germ-cells,  103 
Giacomini's  band,  34 
Globus  pallidus,  48 
Glomeruli  olfactorii,  118 
Glomus  chorioideum.  44 
Glossopharyngeus,  184 
Go'Igi-Holmgren  canals,  113 
Golgi's  network,  112 

cells,   III 
Goll's  column,  90,  164 
Gowers'  tract,  161,  170 
Granule  layer,  cerebellum,  154 

olf.  bulb,  119 
Gratiolet's  optic  radiation,  136,  172 
Gubler's  paralysis,  143 
Gudden's  tegmental  bundle,  147 
Gustatory  centre,  126 

paths,  190 
Gyrus,  or  Gyri,  ambiens,  27 

Andreae  Retzii,  36 

angularis,  21 

centralis  ant.,  19 
post.,  21 

cerebelli,  76 

cinguli,  30 

dentatus,  32,  121,  122 

descendens  (Ecker),  21 

diagonalis,  30 

digitati  e.xterni,  35 

epicallosus,  34 

fasciolaris,  34,  35 

fornicatus,  25,  30,   119 

frontalis,  20 

fusiformis,  24 

hippocampi,  32 

insulae,  22 

intralimbicus,  35 

lingual  is,  24 

occipitales,  21 

olfactorio-orbitalis,  29 


Gyrus  olfact.  lateral.,  27 

medial.,  27 
orbitales,  25 
perforatus,  29 
profundi,  18 
rectus,  25 

rhinenceph. -fusiform.,  32 
rhinenceph. -lingual.,  32 
rhinenceph. -temporales,  32 
semilunaris,  27 

subcallosus   (Zuckerkandl),  30 
subsplenialis,  34 
supramarginalis,  21 
temporales,  21 

transversi,  21 
transitivi,  18 
uncinatus,  35 

Habenula,  55 

Hearing,  cortical  centre.  126 
Helweg's  triangular  tract,  162,  171 
Hemianopsia,  174 
Hemiopia,  174 

Hemiplegia  alternans  oculomot.,  143 
facial.,  143 

completa,  142 

cruciata,  144 

incompleta,  142 
Hemisphaerium,  17 
Heschl's  convolutions,  21 
Hind-brain,  85 

Hippocampus  (cornu  Ammonis),  45,  120 
Hypoglossus,  185 
Hypophysis,  38 
Hypothalamus,  64 

Incisura  praeoccipitalis,  20 

temporalis  (Schwalbe),  24 
Indirect  sensory  cerebellar  tract,  171 
Induseum  griseum,  33,  123 

inferius,  34 
Infundibulum,  37 
Insula,  22 

Interniedius  Wrisbergi,  178 
Inter-brain,  52 
Internal  capsule,  48 
Interolivary   stratum,   117 
Interradial  feltwork,  115 
Intumescentia  cervicalis,  89 

lumbalis,  89 
Island  of  Reil,  22 
Isthmus  gyri  fornicati,  30,  31 

rhombencephali,  4,  70 

Lamina  affixa,  41 

chorioidea  ventric.  lat.,  41 
ventric.  quarti,  79 
ventric.  tertii,  57 


INDEX. 


285 


Lamina  medullaris  circumvoluta,  121 

praecommissuralis,  30 

quadrigemina,  66 

rostralis,  15 

septi  peliucidi,  41 

terminaiis,  15,  37 
Laminae  medullares  cerebelli,  76 

thalami,  60 
Lancisi's  strix,  33 
Lateral  column,  90,  161 

ground  bundle,  162 

nuclei,  85,  170 

pyramidal  tract,  161 

tracts,  90,  161 

ventricle,  40 
Lattice  layer  of  thalamus,  59,  227 
Lemniscus  lateralis,  179,  190 

medialis,  167,  187 
Leptomeninx,  86 
Ligamentum  denticulatum,  94 
Limbic  lobe,  25 
Limbus  Giaconiini,  34 
Limen  insulae,  28 
Lingula  cerebelli,  73 
Liquor  cerebro-spinalis,  8 
Lissauer"s  marginal  zone,  163 
Lobi  cerebelli,  72,  y^,  74 

insulae,  22 
Lobuli  cerebelli,  72,  y^ 
Lobulus  paracentralis,  24 
Lobus  frontalis,  19 

occipitalis,  21 

olfactorius,  26 

olfact.  ant.,  27 
post.,  29 

parietalis,  20 

temporalis.  21 
Locus  caeruleus,  82,  177 
Luys'  body,  60,  228 
Lyra  Davidis,  44,  135 

Mamniillary  bodies,  61 
Mantle  layer,  105 
Marginal  zone,  91 
Martinotti  cells,  115 
Massa  intermedia,  55 
Medial  fillet,  149,  167,  187 
Medulla  obloiigata,  77,  166 

spinalis,  89,  159 
Medullary  groove,   3 

plate,  3 

ridge,  3 

tube,  4 
Membrana  limitans,  102 
Meninges,  86 
Mesencephalon,  4,  66 

summary,  69 
Metathalamus,  63 


Metencephalon,  4,  77 

Meynert  s  fountain  decussation,  153,  273 

Mid-brain,  66 

Middle  commissure,  55 

Mitral  cells.  118 

Molecular  layer,  114,  121,  12?.,  IZ4 

Monakow's  nucleus,  243 

bundle,  153,  162 
Monoplegia.   145 
Monticulns  cerebelli,  73 
Moss  fibres,  155 
Motor  tract,  131,  138,  151,  191 

centre,  124 
Multipolar  cells,  no 
Myelencephalon,  4,  77,  166 

Nerve  process,  108 

cells,  106 
Nervus  abducens,  176 

accessorius,  185 

acusticus,  179 

cochleae,    179 

facialis,  178 

glossopharyngeus,  184 

hypoglossus,  186 

intermedins  (Wrisbergi),  178 

oculomotorius,  175 

olfactorius,  172 

opticus,  172 

Sapolini,  178 

trigeminus,  176 

trochlearis,  176 

vagus,  184 

vestibuli,  iSi 

Wrisbergi,  178 
Neural  or  medullary  tube,  102 
Neurite,  109 
Neuroblasts,  103 
Neurofibrills,  112 
Neuroglia,  103 
Neuroglia  cells,  103,  106 
Neurone,  109 
Nidus  avis,  75 
Nissl's  bodies,  112 
Nodulus,  75 
Nucleus  alae  cinereae,  85,  1S5 

ambiguus,  85,    184 

amygdalae,  50,  145,  219 

arcuati,  84,  170 

caudatus,  47,  144 

corpor.  geniculati,  61 
mamillaris,  61,  147 
trapczoides,  83,  179 

dentatus  cerebelli,  83 

dorsalis  (Clarkii),  91,  157 

emboliformis,  83 

emincntiae  teretis,  263 

fastigii,  83 


286 


INDEX. 


Nucl.  funiculi  cuneati,  84,  167 

gracilis,  84,   167 
globosi,  84 
habenulae,  61,  148 
hypothalamicus,  61 
intercalatus  Staderini,  251 
laterales,  84,  170 
lemnisci,   70,  82,   179 
lenticularis,  48 
lentiforrais,  48,  144 
nervorum,  see  Cerebral  Nerves,  i; 
olivaris  accessor.,  84 

inferior,  84,  170 

superior,  179 
pontis,  82 

praepositus    XII,   255 
respiratorius,  196 
reticularis  lateralis,  243 

tegmenti,  83,  155 
Roller,  251    ■ 
ruber,  69,  137,  155,  227 
salivatorius,  257 
semilunaris  (Flechsig),  60,  227 
tecti,  83 
thalami,  58,  59 

Obex,  78 
Occipital  lobe,  21 
Oculomotorius,  175 
Olfactory  bulb,  27,  118 

bundle,  basal,  149 

centre,  126,  149 

nerve,  118,  172 

path,  190 

tract,  27,  145 

tubercle,  27 
Oliva  inferior,  84,  170 

superior,  83,  179 
Operculum,  22 
Optic  radiation,  172 

tract,  172 
Optico-acoustic  reflex  tract,  153 
Opticus,  172 
Oval  bundle,  166 

Pacchionian  granulations,  88 

Pachymeninx,  86 

Pallium,  18 

Paraplegia,  143 

Parietal  lobe,  20 

Pars  mamillaris  hypothalami,  56 

optica   hypothalami,   ^y 
Pedunculi  cerebri,  66 
Pedunculus  corpor.  mamillaris,  147 

flocculi,  75 
Penicilli  olfactorii,  118 
Pia  mater  cerebri,  88 
spinalis,  93 


Pineal  body,  55 
Pituitary  body,  38 
Plexus  chorioideus  ventric.  lat.,  42 
ventric.  quarti,  80 
ventric.  tertii,  58 
Pons  Varolii,  71 
Pontile  nuclei,  82 
tegmentum,  83 
tracts,  137 
Posterior  column,  163 

comma  bundle,  166 
nuclei,  167 
oval  bundle,  166 
triangular  bundle,  166 
ventral  field,  166 
Posterior  horn  cells,  159 
Post,  longitudinal  bundle,  148,  153,  18 

of  Schiitz,  148,  153,  182 
Praecuneus,  24 

Projection  fibres,  131,  135,  186 
Prosencephalon,  4 
Protoplasmic  processes,  109 
Psalterium,  44 
Pulvinar,  55 
Pupillary  reflex,  173 
Purkinje  cells,  154 
Putamen,  48 
Pyramidal  nuclei,    170 
tracts,  137,  161,  191 
Pyramids,  decussation,  77 
Pyramis  cerebelli,  74 

Quadrate  lobule,  24 

Radiatio  corpor.  callosi,  40 
striati,  144 

strio-subthalamica,  144 

strio-thalamica,  144 
Radicular  zone  of  cord,  163 
Radii,  cortical  fibres,  116 
Randschleier,    105 
Recessus  anterior,  68 

infundibuli,  38 

lateral,  ventric.  quarti,  79 

opticus,  17 

pinealis,  55 

posterior,  68 

suprapinealis,  56 

tecti,  79 

triangularis,  58 
Reflex  collaterals.  131,  166,  i,)?. 
Reflex  conduction,  131,  191 
Regio  subthalamica,  61 
Restiform  body,  158,  170 
Rhinencephalon,  25,  144 
Rhombencephalon,  4,  70 
Roof-nucleus,.  83 
Rostrum.  15 
Rugae  loci  caerulei,  82 


INDEX. 


287 


Saccus  vasculosus,  38 
Sapolini's  nerve,  178 
Schultze's  comma  bundle.  166 
Schiitz's  longitudinal  bundle,  148,  153 
Sensory  centres,  126 

cerebellar  tracts,  170 
speech  centre,  199 
tracts.  186 
Septum  anterius,  93 

cervicale  intermed.,  93 
pellucidum,  16,  41 
subarachnoideale,  93 
Sinus  occipitalis.  87 
petros.  sup.,  87 
rectus,  88 
sagittal.,  87 
transversus,  87 
Smell,  cortical  centre,  126 
Speech  centres,  199 
disturbance,  202 
path,  200 
Spinal  cord,  159 
cells,  160 
development,  8 
membranes,  93 
tracts,  161 
Spongioblasts,  103 
Spongiopilemma,  106 
Stratum  gelatinosum,  118 

granulosum,  115,  119,  122,  154 
griseum  centrale,  68,  225 

colliculi  sup.,  69 
lacunosum,  121 
lucidum.  121 

molcculare,  114,  118,  121,  122,  154 
oriens,  121 
radiatum,  121 
reticulare,  60,  227 
zonale,  54 
Stria  alba  tuberis   (Lenhossek),  57,  146 
cornea,  41 
medullaris,  54,  148 
olfactoria  lat.,  29,  145 

med.,  27,  145 
terminalis,  41 
Striae  acusticae,  81,  179 
Lancisii,  33,  40,  14s 
longitudinales  fcorp.  callosi),  40 
medullarcs  or  acusticae,  81,  179 
Stripe  of  Baillarger,  39 
sennari,  39 
Vicq  d'Azyr,  39 
Subarachnoidal  space,  86,  88 

tissue,  88 
Subdural  space,  86 
Subiculum,  45 
Subpial  space,  88 


Substantia  cortical,  cerebelli,  83,  154 
cerebri,  38,  114 
gelatinosa  centralis,  gi 

Rolandi,  91 
nigra  (Sommering),  67 
perforata  ant.,  29,  145 

post.,  68 
reticularis  alba,  247 

(Arnold),  32,  121 
grisea,  241,  247 
Sulcus  OT  sulci  arcuat.  rhinencephali,  ^ 
basilaris  (pontis),  71 
centralis  insulae,  22 

Rolandi,  19 
cerebelli,  72,  73,  74,  75 
chorioideus,  54 
cinguli,  23 

circularis  (Reili),  22 
corpor.  callosi,  23 
dentato-fasciolaris,  34 
digitati  externi,  35 
fimbrio-dentat.,  33 
frontales,  19 

hypothalamicus  (Monroi),  16,  55 
interdigitales,  43 
intermedius,  41 
post.,  go 

primus  (Jensen),  21 
secundus  (Eberstaller),  21 
interparietalis,  20 
lateralis  ant..  89 

post.,  89 
limitans,  82 
median,  fornicis,  44 

fossae  rhomboid.,  81 
post.,  8g 
mesencephali  lat.,  68 

med.,  68 
Monroi.  16,  55 
nervi  oculomotorii,  67 
occipitales,  21 
occipitalis  transvers.,  20,  21 
olfactorius,  25 
orbitales,  25 
paracentralis,  23 

parietal,  transvers.   (Brissaud),  21 
parolfact.  ant.,  27 

post.,  26 
postcentralis,  20 
praecentralis,    19 
radiatus,  19 
semiannularis,  28 
subcallos.  med.,  30 
subparietal.,  23 
supraorbital.  (Broca),  23 
tcmporales,  21 
Supraradial  feltwork.  116 
Sylvian  aqueduct,  68 


INDEX. 


Sylvian  fissure,  18 

*ossa,  18 

valley,  18 
System  of  Deiters'  nucleus,  181 

Taenia  cliorioidea,  42 
fimbriae,  44 
fornicis,  42 
pontis,  71 

semicircularis,  146,  214 
tecta,  33,  40 
thalami,  58 
ventriculi  quarti.  80 

Taeniae,  42 

Tapetum,  43 

Taste,  cortical  centre,  126 
paths,  189 

Tegmen  fossae  rhomboid.,  "jg 

Tegmental  decussation,  153,  273 
tract,  central,  151 

Tegmentum,  67 
pontis,  83 

Tela  chorioidea  ventric.  quarti,  79 
ventric.  tertii,  52,  57 

Telencephalon,  17,  134 

internal  configuration,  38 

Telodendrion,  109 

Temporal  lobe,  21 

Tentorium  cerebelli,  87 

Thalamencephalon,  54 

Thalamus,  54,  58 

Third  ventricle,  57 

Tigroid,  112 

Tonsilla,  75 

Torcular  Herophili,  88 

Tracts,  projection,  186 

Tract,  bulbo-thalaniicus,  151,  167 
cerebello-bulbaris,  170 
cerebello-tegmentalis,  150,  156 
cerebro-spinalis,  138,  i6r 
cervico-lumbalis  dorsal.,  166 
corticis  ad  pontem,  137 
cortico-habenularis,  146,  148 
cortico-mamillaris,  146 
cortico-tectales,  153 
cortico-tegmentalis,   136 
cortico-thalamici,  150 
fastigio-bulbaris,  171,  259 
habenulo-peduncularis,  148 
mamillo-tegmentalis,  147 
mamillo-thalamicus,  147 
nucleo-cerebellaris,  170,  181 
olfacto^ammonicus,  215 
olfacto-habenularis,   148 
olfacto-mesencephalic,   149 
olfactorius,  27,  145 
olivo-cerebellaris,  170 


Tract,  opticus,  13,  172 

peduncularis  transvers.,  68 

ponto-cerebellares,  137,  155 

rubro-reticularis,  153 

rubro-spinalis   (Monakow),  153,  162 

rubro-thalamicus,  151 

soKtarius,  185 

spinalis  N.  V.,  178 

spino-cerebellaris  dorsal.   (Flechsig),  161,  170 
ventral.  (Gowers),  70,  161,  170 

spino-olivaris  (Helweg),  162,  170 

spino-tectalis,  153,  163 

spino-thalamicus,  151,  163,  169,  186 

tecto-bulbaris,  153 

tecto-cerebellares,  153 

tecto-pontinus   (Miinzer),  153,  269 

tecto-reticularis  (Pavlow),  153 

tecto-spinalis,  153,  161,  163 

tegmento-mamillaris,  147 

thalamo-corticales,  135,  150 

thalamo-habenularis,     148 

thalamo-mamillaris,  147 

thalamo-olivaris,  151,  171 

thalamo-spinalis,  151,  163 

uncinatus,  171,  259 

vestibulo-spinalis,  161,  163,  181 
Trigeminus,  176 
Trigonum  coUaterale,  43 

habenulae,  55 

lemnisci,  70 

nervi  hypoglossi,  82 

olfactorium,  27 

praecommissurale,  30 

subpineale,  66 
Trochlearis,  176 
Truncus  cerebri,  8 
Tuber  cinereum,  37 

valvulae,  74 

vermis,  74 
Tuberculum  acusticum,  82,  179 

cinereum,  79 

cuneatum,  79 

mamillare  laterale,  57 

olfactorium,  27 

thalami  ant.,  59 

Uncus,  35 
Unipolar  cells,  no 
Uvula,  7S 

Vagus,  184 
Vallecula  cerebelli,  72 

lateralis,  18 
Velum  interpositum,  57 
Velum  medullare  ant.,  70 
post.,  75 

terminale  (Abbey),  34,  44 


INDEX. 


289 


Vena  cerebri  interna,  58 

magna  (Galeni).  58 

chorioidea,  58 

septi  pellucidi,  58 

terminalis,  58 
Ventral  field  of  cord.  166 
Ventriculus  Arantii,  81 

lateralis.  40 

quartus.  79 

terminalis   (Krause),  91 

tertius,  57 
Verga's  ventricle,  44 
Vermis  cerebelli,  ~2 
Verrucae  gA'ri  hippocampi,  32 
Vestibularis,  181 


Vicq  d'Azyr's  stripe,  40 

bundle,  147 
Vinculum    lingulae,    73 
Visual  centre,  127 

path,   191 
Visuo-auditory  path,  196 

Weber's  paralysis,  143 
Wernekink's  commissure,  271 
Wernicke's  centre,  129 

field.  60,   229 

pupillary  reaction,  174 
Wrisberg's  nerve.   178 
Writing  centres.  202 

Zona  incerta.  224,  225 


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